Literal movement code may grow auto litpool so big that it won't be
possible to jump around it. Limit the size of auto litpools by 1/2 of
the jump range.
gas/
2018-02-20 Max Filippov <jcmvbkbc@gmail.com>
* config/tc-xtensa.c (struct litpool_frag): Add new field
literal_count.
(MAX_AUTO_POOL_LITERALS, MAX_EXPLICIT_POOL_LITERALS)
(MAX_POOL_LITERALS): New macro definitions.
(auto_litpool_limit): Initialize to 0.
(md_parse_option): Set auto_litpool_limit in the presence of
--auto-litpools option.
(xtensa_maybe_create_literal_pool_frag): Zero-initialize
literal_count field.
(xg_find_litpool): New function. Make sure that found literal
pool size is within the limit.
(xtensa_move_literals): Extract literal pool search code into
the new function.
* testsuite/gas/xtensa/all.exp: Add auto-litpools-2 test.
* testsuite/gas/xtensa/auto-litpools-2.d: New file.
* testsuite/gas/xtensa/auto-litpools-2.s: New file.
* testsuite/gas/xtensa/auto-litpools.d: Fix up changed
addresses.
* testsuite/gas/xtensa/auto-litpools.s: Change literal value so
that objdump doesn't get out of sync.
For jumps requiring multiple trampolines trampoline placement code may
place multiple sequential trampolines into the same frag. Don't do that.
gas/
2018-02-13 Max Filippov <jcmvbkbc@gmail.com>
* config/tc-xtensa.c (xg_find_best_trampoline): Skip trampoline
frag that contains source address.
Don't use address where symbol gets resolved, as during section
relaxation symbols will slide, instead canonicalize symbols and check
that they are are the same.
This fixes a bug when a relaxed jump goes into the wrong trampoline.
gas/
2017-12-07 Max Filippov <jcmvbkbc@gmail.com>
* config/tc-xtensa.c (xg_order_trampoline_chain): Replace
xg_order_trampoline_chain_entry call with check for
canonicalized symbol equality and offset equality.
find_trampoline_seg takes noticeable time when assembling source with
many sections. Cache the result of the most recent search and check it
first. No functional changes.
gas/
2017-11-27 Max Filippov <jcmvbkbc@gmail.com>
* config/tc-xtensa.c (find_trampoline_seg): Add static variable
that caches the result of the most recent search.
There is a recurring pattern in assembly files generated by a compiler
where a lot of jumps in a function are going to the same place. When
these jumps are relaxed with trampolines the assembler generates a
separate jump thread from each source.
Create an index of trampoline jump targets for each segment and see if a
jump being relaxed goes to a location from that index, in which case
replace its target with a location of existing trampoline jump that
results in the shortest path to the original target.
gas/
2017-11-27 Max Filippov <jcmvbkbc@gmail.com>
* config/tc-xtensa.c (trampoline_chain_entry, trampoline_chain)
(trampoline_chain_index): New structures.
(trampoline_index): Add chain_index field.
(xg_order_trampoline_chain_entry, xg_sort_trampoline_chain)
(xg_find_chain_entry, xg_get_best_chain_entry)
(xg_order_trampoline_chain, xg_get_trampoline_chain)
(xg_find_best_eq_target, xg_add_location_to_chain)
(xg_create_trampoline_chain, xg_get_single_symbol_slot): New
functions.
(xg_relax_fixups): Call xg_find_best_eq_target to adjust jump
target to point to an existing jump. Call
xg_create_trampoline_chain to create new jump target. Call
xg_add_location_to_chain to add newly created trampoline jump
to the corresponding chain.
(add_jump_to_trampoline): Extract loop searching for a single
slot with a symbol into a separate function, replace that code
with a call to that function.
(relax_frag_immed): Call xg_find_best_eq_target to adjust jump
target to point to an existing jump.
* testsuite/gas/xtensa/all.exp: Add trampoline-2 test.
* testsuite/gas/xtensa/trampoline.d: Adjust absolute addresses
as many duplicate trampoline chains are now coalesced.
* testsuite/gas/xtensa/trampoline.s: Add _nop so that objdump
stays in sync with instruction stream.
* testsuite/gas/xtensa/trampoline-2.l: New test result file.
* testsuite/gas/xtensa/trampoline-2.s: New test source file.
There's almost exact copy of the trampoline placement code in the
search_trampolines function that is used for jumps generated for relaxed
branch instructions. Get rid of the duplication and reuse
xg_find_best_trampoline function for that.
gas/
2017-11-27 Max Filippov <jcmvbkbc@gmail.com>
* config/tc-xtensa.c (search_trampolines, get_best_trampoline):
Remove definitions.
(xg_find_best_trampoline_for_tinsn): New function.
(relax_frag_immed): Replace call to get_best_trampoline with a
call to xg_find_best_trampoline_for_tinsn.
* testsuite/gas/xtensa/trampoline.d: Adjust absolute addresses
as the placement of trampolines for relaxed branches has been
changed.
Replace linked list of trampoline frags with an ordered array, so that
instead of indexing fixups trampolines could be indexed. Keep each array
in the trampoline_seg structure, so there's no need to rebuild it for
every new processed segment. Don't run relaxation for each trampoline
frag, instead run it for each fixup in the current segment that needs
relaxation at the beginning of each relaxation pass. This way the
complexity of this process drops from about O(n^2 * m) to about
O(log n * m), where n is the number of trampoline frags and m is the
number of fixups that need relaxation in the segment.
gas/
2017-11-27 Max Filippov <jcmvbkbc@gmail.com>
* config/tc-xtensa.c (trampoline_index): New structure.
(trampoline_seg): Replace trampoline list with trampoline index.
(xg_find_trampoline, xg_add_trampoline_to_index)
(xg_remove_trampoline_from_index, xg_add_trampoline_to_seg)
(xg_is_trampoline_frag_full, xg_get_fulcrum)
(xg_find_best_trampoline, xg_relax_fixup, xg_relax_fixups)
(xg_is_relaxable_fixup): New functions.
(J_MARGIN): New macro.
(xtensa_create_trampoline_frag): Use xg_add_trampoline_to_seg
instead of open-coded addition to the linked list.
(dump_trampolines): Iterate through the trampoline_seg::index.
(cached_fixupS, cached_fixup, fixup_cacheS, fixup_cache)
(fixup_order, xtensa_make_cached_fixup)
(xtensa_realloc_fixup_cache, xtensa_cache_relaxable_fixups)
(xtensa_find_first_cached_fixup, xtensa_delete_cached_fixup)
(xtensa_add_cached_fixup, check_and_update_trampolines): Remove
definitions.
(xg_relax_trampoline): Extract logic into separate functions,
replace body with a call to xg_relax_fixups.
(search_trampolines): Replace search in linked list with search
in index. Change data type of address-tracking variables from
int to offsetT. Replace abs with labs.
(xg_append_jump): Finish the trampoline frag if it's full.
(add_jump_to_trampoline): Remove trampoline frag from the index
if the frag is full.
* config/tc-xtensa.h (xtensa_frag_type): Remove next_trampoline.
* testsuite/gas/xtensa/trampoline.d: Adjust absolute addresses
as the placement of trampolines has slightly changed.
* testsuite/gas/xtensa/trampoline.s: Add _nop so that objdump
stays in sync with instruction stream.
The split between fragS and trampoline_frag doesn't save much space, but
makes trampolines management much more awkward. Merge trampoline_frag
data into the xtensa_frag_type, which is a part of fragS. No functional
changes.
gas/
2017-11-27 Max Filippov <jcmvbkbc@gmail.com>
* config/tc-xtensa.c (init_trampoline_frag): Replace pointer to
struct trampoline_frag parameter with pointer to fragS.
(xg_append_jump): Remove jump_around parameter.
(struct trampoline_frag): Remove.
(struct trampoline_seg): Change type of trampoline_list from
struct trampoline_frag to fragS.
(xtensa_create_trampoline_frag): Don't allocate struct
trampoline_frag. Initialize new fragS::tc_frag_data fields.
(dump_trampolines, xg_relax_trampoline, search_trampolines)
(get_best_trampoline, init_trampoline_frag)
(add_jump_to_trampoline, relax_frag_immed): Replace pointer to
struct trampoline_frag with a pointer to fragS.
(xg_append_jump): Remove jump_around parameter, use
fragS::tc_frag_data.jump_around_fix instead.
(xg_relax_trampoline, init_trampoline_frag)
(add_jump_to_trampoline): Don't pass jump_around parameter to
xg_append_jump.
* config/tc-xtensa.h (struct xtensa_frag_type): Add new fields:
needs_jump_around, next_trampoline and jump_around_fix.
xtensa_create_trampoline_frag has opencoded fragment equivalent to
find_trampoline_seg. Drop the fragment and use find_trampoline_seg
instead. No functional changes.
gas/
2017-11-27 Max Filippov <jcmvbkbc@gmail.com>
* config/tc-xtensa.c (find_trampoline_seg): Move above the first
use.
(xtensa_create_trampoline_frag): Replace trampoline seg search
code with a call to find_trampoline_seg.
init_trampoline_frag, add_jump_to_trampoline and xg_relax_trampoline add
a jump to the end of a trampoline frag. Extract it into a separate
funciton and use it in all these places. No functional changes.
gas/
2017-11-27 Max Filippov <jcmvbkbc@gmail.com>
* config/tc-xtensa.c (xg_append_jump): New function.
(xg_relax_trampoline, init_trampoline_frag)
(add_jump_to_trampoline): Replace trampoline jump assembling
code with a call to xg_append_jump.
To make measurement and changes easier extract trampoline relaxation
function. No functional changes.
gas/
2017-11-27 Max Filippov <jcmvbkbc@gmail.com>
* config/tc-xtensa.c (xg_relax_trampoline): New function.
(xtensa_relax_frag): Replace trampoline relaxation code with a
call to xg_relax_trampoline.
Get rid of the assumption that XCHAL_* macros are preprocessor
constants: don't use them in preprocessor conditionals or in static
variable initializers.
2017-06-14 Max Filippov <jcmvbkbc@gmail.com>
bfd/
* elf32-xtensa.c (elf_xtensa_be_plt_entry,
elf_xtensa_le_plt_entry): Add dimension for the ABI to arrays,
keep both windowed and call0 ABI PLT definitions.
(elf_xtensa_create_plt_entry): Use selected ABI to choose upper
elf_xtensa_*_plt_entry endex.
(ELF_MAXPAGESIZE): Fix at minimal supported MMU page size.
gas/
* config/tc-xtensa.c (density_supported, xtensa_fetch_width,
absolute_literals_supported): Leave definitions uninitialized.
(directive_state): Leave entries for directive_density and
directive_absolute_literals initialized to false.
(xg_init_global_config, xtensa_init): New functions.
* config/tc-xtensa.h (TARGET_BYTES_BIG_ENDIAN): Define as 0.
(HOST_SPECIAL_INIT): New definition.
(xtensa_init): New declaration.
* config/tc-xtensa.c (xtensa_maybe_create_literal_pool_frag):
Initialize lps->frag_count with auto_litpool_limit.
(xg_promote_candidate_litpool): New function.
(xtensa_move_literals): Extract candidate litpool promotion code
into separate function. Call it for all possible found
candidates.
(xtensa_switch_to_literal_fragment): Drop 'recursive' flag and
call to xtensa_mark_literal_pool_location that it guards.
Replace it with call to xtensa_maybe_create_literal_pool_frag.
Initialize pool_location with created literal pool candidate.
* testsuite/gas/xtensa/all.exp: Add new tests.
* testsuite/gas/xtensa/auto-litpools-first1.d: New test results.
* testsuite/gas/xtensa/auto-litpools-first1.s: New test.
* testsuite/gas/xtensa/auto-litpools-first2.d: New test results.
* testsuite/gas/xtensa/auto-litpools-first2.s: New test.
* testsuite/gas/xtensa/auto-litpools.d: Fix offsets changed due
to additional jump instruction.
add_jump_to_trampoline assumes that jump instruction is in slot 0,
when it's in other slot that results in fixup that references NULL symbol,
which results in segfault later in xtensa_make_cached_fixup.
Search for the non-NULL symbol in the tc_frag_data.slot_symbols and check
that there's exactly one such slot.
xtensa_relax_frag for RELAX_TRAMPOLINE reassigns fixup from the original
instruction with jump to generated jump in the trampoline frag, but does not
fix its fx_r_type or fx_size. That results in "undecodable fix" or
"fixup not contained within frag" error messages during relaxation.
Fix both these fields.
gas/
2017-03-22 Max Filippov <jcmvbkbc@gmail.com>
* config/tc-xtensa.c (xtensa_relax_frag): Change fx_size of the
reassigned fixup to size of jump instruction (3) and fx_r_type
to BFD_RELOC_XTENSA_SLOT0_OP, as there's only one slot.
(add_jump_to_trampoline): Search
origfrag->tc_frag_data.slot_symbols for the slot with non-NULL
symbol and use that slot instead of slot 0.
There's no reason to define these macros twice.
gas/ChangeLog:
2016-06-22 Trevor Saunders <tbsaunde+binutils@tbsaunde.org>
* config/tc-xtensa.c: Include elf/xtensa.h.
It always returns an element of the enum operatorT, so it should be clearer to
make that the return type.
gas/ChangeLog:
2016-05-24 Trevor Saunders <tbsaunde+binutils@tbsaunde.org>
* config/tc-xtensa.c (struct suffix_reloc_map): Change type of field
operator to operatorT.
(map_suffix_reloc_to_operator): Change return type to operatorT.
Xtensa uses it in several macros passing it a literal string, so its convenient
for the argument type to be const char *. However some of the code in
symbols.c seems to assume tc_canonicalize_symbol_name () will return a non
const pointer, and some other target's implementations even modify the
argument, so it seems best to return a char * which means casting away const on
the argument when we return it instead of another string.
gas/ChangeLog:
2016-03-31 Trevor Saunders <tbsaunde+binutils@tbsaunde.org>
* config/tc-xtensa.c (struct rename_section_struct): Make old_name
const.
(xtensa_section_rename): Make argument type const char *.
* config/tc-xtensa.h (xtensa_section_rename): Adjust.
Despite the documentation and the comment in xtensa_move_literals, in
the presence of --text-section-literals and --auto-litpools literals are
moved from the separate literal sections into .init and .fini, because
the check in the xtensa_move_literals is incorrect.
This moving was broken with introduction of auto litpools: some literals
now may be lost. This happens because literal frags emitted from .init
and .fini are not closed when new .literal_position marks new literal
pool. Then frag_align(2, 0, 0) changes type of the last literal frag to
rs_align. rs_align frags are skipped in the xtensa_move_literals. As a
result fixups against such literals are not moved out of .init.literal/
.fini.literal sections producing the following assembler error:
test.S: Warning: fixes not all moved from .init.literal
test.S: Internal error!
Fix check for .init.literal/.fini.literal in the xtensa_move_literals
and don't let it move literals from there in the presence of
--text-section-literals or --auto-litpools.
2016-02-17 Max Filippov <jcmvbkbc@gmail.com>
gas/
* config/tc-xtensa.c (xtensa_move_literals): Fix check for
.init.literal/.fini.literal section name.
* testsuite/gas/xtensa/all.exp: Add init-fini-literals to the
list of xtensa tests.
* testsuite/gas/xtensa/init-fini-literals.d: New file:
init-fini-literals test result patterns.
* testsuite/gas/xtensa/init-fini-literals.s: New file:
init-fini-literals test.
Change 1058c7532d "Use signed data type for R_XTENSA_DIFF* relocation
offsets." changed signedness of BFD_RELOC_XTENSA_DIFF* relocations
substituted for BFD_RELOC_*. This made it impossible to encode arbitrary
8-, 16- and 32-bit values, which broke e.g. debug info encoding by .loc
directive. Revert this part and add test.
gas/
2016-02-03 Max Filippov <jcmvbkbc@gmail.com>
* config/tc-xtensa.c (md_apply_fix): Mark BFD_RELOC_XTENSA_DIFF*
substitutions for BFD_RELOC_* as unsigned.
* gas/testsuite/gas/xtensa/all.exp: Add loc to list of xtensa
tests.
* gas/testsuite/gas/xtensa/loc.d: New file: loc test result
patterns.
* gas/testsuite/gas/xtensa/loc.s: New file: loc test.
Auto-litpools is the automated version of text-section-literals: literal
pool candidate frags are planted every N frags and during relaxation
they are turned into actual literal pools where literals are moved to
become reachable for their first reference by L32R instruction.
2015-08-12 David Weatherford <weath@cadence.com>
gas/
* config/tc-xtensa.c (struct litpool_frag, struct litpool_seg):
New structures.
(xtensa_maybe_create_literal_pool_frag): New function.
(litpool_seg_list, auto_litpools, auto_litpool_limit)
(litpool_buf, litpool_slotbuf): New static variables.
(option_auto_litpools, option_no_auto_litpools)
(option_auto_litpool_limit): New enum identifiers.
(md_longopts): Add entries for auto-litpools, no-auto-litpools
and auto-litpool-limit.
(md_parse_option): Handle option_auto_litpools,
option_no_auto_litpools and option_auto_litpool_limit.
(md_show_usage): Add help for --[no-]auto-litpools and
--auto-litpool-limit.
(xtensa_mark_literal_pool_location): Record a place for literal
pool with a call to xtensa_maybe_create_literal_pool_frag.
(get_literal_pool_location): Find highest priority literal pool
or convert candidate to literal pool when auto-litpools are used.
(xg_assemble_vliw_tokens): Create literal pool after jump
instruction.
(xtensa_check_frag_count): Create candidate literal pool every
auto_litpool_limit frags.
(xtensa_relax_frag): Add jump around literals to non-empty
literal pool.
(xtensa_move_literals): Estimate literal pool addresses and move
unreachable literals closer to their users, converting candidate
to literal pool if needed.
(xtensa_switch_to_non_abs_literal_fragment): Only emit error
about missing .literal_position in case auto-litpools are not
used.
* config/tc-xtensa.h (xtensa_relax_statesE): New relaxation
state: RELAX_LITERAL_POOL_CANDIDATE_BEGIN.
* doc/as.texinfo (Xtensa options): Document --auto-litpools and
--no-auto-litpools options.
* doc/c-xtensa.texi (Xtensa options): Likewise.
2015-08-12 Max Filippov <jcmvbkbc@gmail.com>
gas/testsuite/
* gas/xtensa/all.exp: Add auto-litpools to the list of xtensa
tests.
* gas/xtensa/auto-litpools.s: New file: auto-litpools test.
* gas/xtensa/auto-litpools.s: New file: auto-litpools test
result pattern.
When --text-section-literals is used and code in the .init or .fini
emits literal in the absence of .literal_position, xtensa_move_literals
segfaults.
Check that search_frag is non-NULL in the xtensa_move_literals and
report error otherwise.
2015-05-26 Max Filippov <jcmvbkbc@gmail.com>
gas/
* config/tc-xtensa.c (xtensa_move_literals): Check that
search_frag is non-NULL. Report error if literal frag is not
found.
Extra condition 'abs (addr - trampaddr) < J_RANGE / 2' for trampoline
selection results in regressions: when relaxable jump is little longer
than J_RANGE so that single trampoline makes two new jumps, one longer
than J_RANGE / 2 and one shorter, correct trampoline cannot be found.
Drop that condition.
2015-05-13 Max Filippov <jcmvbkbc@gmail.com>
gas/
* config/tc-xtensa.c (xtensa_relax_frag): Allow trampoline to be
closer than J_RANGE / 2 to jump frag.
gas/testsuite/
* gas/xtensa/trampoline.s: Add regression testcase.
Currently every fixup in the current segment is checked when relaxing
trampoline frag. This is very expensive. Make a searchable array of
fixups pointing at potentially oversized jumps at the beginning of every
relaxation pass and only check subset of this cache in the reach of
single jump from the trampoline frag currently being relaxed.
Original profile:
% time self children called name
-----------------------------------------
370.16 593.38 12283048/12283048 relax_segment
98.4 370.16 593.38 12283048 xtensa_relax_frag
58.91 269.26 2691463834/2699602236 xtensa_insnbuf_from_chars
68.35 68.17 811266668/813338977 S_GET_VALUE
36.85 29.51 2684369246/2685538060 xtensa_opcode_decode
28.34 8.84 2684369246/2685538060 xtensa_format_get_slot
12.39 5.94 2691463834/2699775044 xtensa_format_decode
0.03 4.60 4101109/4101109 relax_frag_for_align
0.18 1.76 994617/994617 relax_frag_immed
0.07 0.09 24556277/24851220 new_logical_line
0.06 0.00 12283048/14067410 as_where
0.04 0.00 7094588/15460506 xtensa_format_num_slots
0.00 0.00 1/712477 xtensa_insnbuf_alloc
-----------------------------------------
Same data, after optimization:
% time self children called name
-----------------------------------------
0.51 7.47 12283048/12283048 relax_segment
58.0 0.51 7.47 12283048 xtensa_relax_frag
0.02 4.08 4101109/4101109 relax_frag_for_align
0.18 1.39 994617/994617 relax_frag_immed
0.01 0.98 555/555 xtensa_cache_relaxable_fixups
0.21 0.25 7094588/16693271 xtensa_insnbuf_from_chars
0.06 0.12 24556277/24851220 new_logical_line
0.06 0.00 7094588/15460506 xtensa_format_num_slots
0.02 0.04 7094588/16866079 xtensa_format_decode
0.05 0.00 12283048/14067410 as_where
0.00 0.00 1/712477 xtensa_insnbuf_alloc
0.00 0.00 93808/93808 xtensa_find_first_cached_fixup
-----------------------------------------
2015-05-02 Max Filippov <jcmvbkbc@gmail.com>
gas/
* config/tc-xtensa.c (cached_fixupS, fixup_cacheS): New typedefs.
(struct cached_fixup, struct fixup_cache): New structures.
(fixup_order, xtensa_make_cached_fixup),
(xtensa_realloc_fixup_cache, xtensa_cache_relaxable_fixups),
(xtensa_find_first_cached_fixup, xtensa_delete_cached_fixup),
(xtensa_add_cached_fixup): New functions.
(xtensa_relax_frag): Cache fixups pointing at potentially
oversized jumps at the beginning of every relaxation pass. Only
check subset of this cache in the reach of single jump from the
trampoline frag currently being relaxed.
For conditional branches that need more than one trampoline to reach its
target assembler couldn't always find suitable trampoline because
post-loop condition check was placed inside the loop, resulting in
premature loop termination. Move check outside the loop.
This fixes the following build errors seen when assembling huge files
produced by gcc:
Error: jump target out of range; no usable trampoline found
Error: operand 1 of 'j' has out of range value '307307'
2014-11-25 Max Filippov <jcmvbkbc@gmail.com>
gas/
* config/tc-xtensa.c (search_trampolines): Move post-loop
condition check outside the search loop.
gas/testsuite/
* gas/xtensa/trampoline.d: Add expected output for branches.
* gas/xtensa/trampoline.s: Add test case for branches.
R_XTENSA_DIFF relocation offsets are in fact signed. Treat them as such.
Add testcase that examines ld behaviour on R_XTENSA_DIFF relocation
changing sign during relaxation.
2014-05-02 Volodymyr Arbatov <arbatov@cadence.com>
David Weatherford <weath@cadence.com>
Max Filippov <jcmvbkbc@gmail.com>
bfd/
* elf32-xtensa.c (relax_section): treat R_XTENSA_DIFF* relocations as
signed.
gas/
* config/tc-xtensa.c (md_apply_fix): mark BFD_RELOC_XTENSA_DIFF*
fixups as signed.
ld/testsuite/
* ld-xtensa/diff_overflow.exp, * ld-xtensa/diff_overflow1.s,
* ld-xtensa/diff_overflow2.s: Add test for DIFF* relocation
signedness and overflow checking.
Linking object files produced by partial linking with link-time
relaxation enabled sometimes fails with the following error message:
dangerous relocation: call8: misaligned call target: (.text.unlikely+0x63)
This happens because no basic block with an XTENSA_PROP_ALIGN flag in the
property table is generated for the first basic block, even if the
.align directive is present.
It was believed that the first frag alignment could be derived from the
section alignment, but this was not implemented for the partial linking
case: after partial linking first frag of a section may become not
first, but no additional alignment frag is inserted before it.
Basic block for such frag may be merged with previous basic block into
extended basic block during relaxation pass losing its alignment
restrictions.
Fix this by always recording alignment for the first section frag.
2014-04-22 Max Filippov <jcmvbkbc@gmail.com>
gas/
* config/tc-xtensa.c (xtensa_handle_align): record alignment for the
first section frag.
gas/testsuite/
* gas/xtensa/all.exp: Add test for the first section frag alignment.
* gas/xtensa/first_frag_align.d: First section frag alignment expected
dump.
* gas/xtensa/first_frag_align.s: First section frag alignment test
source.
Max Filippov
Alan Modra
Nick Clifton
Ambrogino Modigliani
Trevor Saunders
H.J. Lu
Volodymyr Arbatov
David Weatherford