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PR 4029

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* write.c (relax_segment): Insert extra alignment padding
	to break infinite relax loop when given impossible
	gcc_except_table assembly.
This commit is contained in:
Alan Modra 2007-03-14 11:03:38 +00:00
parent d796c0adf2
commit d1c5f15864
2 changed files with 97 additions and 7 deletions
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7
gas/ChangeLog
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@ -1,3 +1,10 @@
2007-03-14 Alan Modra <amodra@bigpond.net.au>
PR 4029
* write.c (relax_segment): Insert extra alignment padding
to break infinite relax loop when given impossible
gcc_except_table assembly.
2007-03-12 H.J. Lu <hongjiu.lu@intel.com>
* config/tc-i386.c (md_assemble): Use Opcode_XXX instead of XXX

97
gas/write.c
View File

@ -1960,13 +1960,38 @@ relax_segment (struct frag *segment_frag_root, segT segment, int pass)
/* Do relax(). */
{
unsigned long max_iterations;
offsetT stretch; /* May be any size, 0 or negative. */
/* Cumulative number of addresses we have relaxed this pass.
We may have relaxed more than one address. */
int stretched; /* Have we stretched on this pass? */
/* This is 'cuz stretch may be zero, when, in fact some piece of code
grew, and another shrank. If a branch instruction doesn't fit anymore,
we could be scrod. */
/* Cumulative address adjustment. */
offsetT stretch;
/* Have we made any adjustment this pass? We can't just test
stretch because one piece of code may have grown and another
shrank. */
int stretched;
/* Most horrible, but gcc may give us some exception data that
is impossible to assemble, of the form
.align 4
.byte 0, 0
.uleb128 end - start
start:
.space 128*128 - 1
.align 4
end:
If the leb128 is two bytes in size, then end-start is 128*128,
which requires a three byte leb128. If the leb128 is three
bytes in size, then end-start is 128*128-1, which requires a
two byte leb128. We work around this dilemma by inserting
an extra 4 bytes of alignment just after the .align. This
works because the data after the align is accessed relative to
the end label.
This counter is used in a tiny state machine to detect
whether a leb128 followed by an align is impossible to
relax. */
int rs_leb128_fudge = 0;
/* We want to prevent going into an infinite loop where one frag grows
depending upon the location of a symbol which is in turn moved by
@ -2089,6 +2114,49 @@ relax_segment (struct frag *segment_frag_root, segT segment, int pass)
}
growth = newoff - oldoff;
/* If this align happens to follow a leb128 and
we have determined that the leb128 is bouncing
in size, then break the cycle by inserting an
extra alignment. */
if (growth < 0
&& (rs_leb128_fudge & 16) != 0
&& (rs_leb128_fudge & 15) >= 2)
{
segment_info_type *seginfo = seg_info (segment);
struct obstack *ob = &seginfo->frchainP->frch_obstack;
struct frag *newf;
newf = frag_alloc (ob);
obstack_blank_fast (ob, fragP->fr_var);
obstack_finish (ob);
memcpy (newf, fragP, SIZEOF_STRUCT_FRAG);
memcpy (newf->fr_literal,
fragP->fr_literal + fragP->fr_fix,
fragP->fr_var);
newf->fr_type = rs_fill;
newf->fr_fix = 0;
newf->fr_offset = (((offsetT) 1 << fragP->fr_offset)
/ fragP->fr_var);
if (newf->fr_offset * newf->fr_var
!= (offsetT) 1 << fragP->fr_offset)
{
newf->fr_offset = (offsetT) 1 << fragP->fr_offset;
newf->fr_var = 1;
}
/* Include growth of new frag, because rs_fill
frags don't normally grow. */
growth += newf->fr_offset * newf->fr_var;
/* The new frag address is newoff. Adjust this
for the amount we'll add when we process the
new frag. */
newf->fr_address = newoff - stretch - growth;
newf->relax_marker ^= 1;
fragP->fr_next = newf;
#ifdef DEBUG
as_warn (_("padding added"));
#endif
}
}
break;
@ -2228,8 +2296,23 @@ relax_segment (struct frag *segment_frag_root, segT segment, int pass)
{
stretch += growth;
stretched = 1;
if (fragP->fr_type == rs_leb128)
rs_leb128_fudge += 16;
else if (fragP->fr_type == rs_align
&& (rs_leb128_fudge & 16) != 0
&& stretch == 0)
rs_leb128_fudge += 16;
else
rs_leb128_fudge = 0;
}
}
if (stretch == 0
&& (rs_leb128_fudge & 16) == 0
&& (rs_leb128_fudge & -16) != 0)
rs_leb128_fudge += 1;
else
rs_leb128_fudge = 0;
}
/* Until nothing further to relax. */
while (stretched && -- max_iterations);