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Explain why we don't make use of RDPC in the sparc PIC register setup.

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* sysdeps/unix/sparc/sysdep.h: Document why we don't use
	"rd %pc" in the PIC register setup sequences.
This commit is contained in:
David S. Miller 2012-02-21 15:45:17 -08:00
parent 3d2b3019e0
commit 0722d7c2ac
2 changed files with 6 additions and 0 deletions
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ChangeLog
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@ -1,5 +1,8 @@
2012-02-20 David S. Miller <davem@davemloft.net>
* sysdeps/unix/sparc/sysdep.h: Document why we don't use
"rd %pc" in the PIC register setup sequences.
* sysdeps/sparc/crti.S: Try to use GOTDATA relocs.
* sysdeps/sparc/sparc32/dl-machine.h (RTLD_START): Likewise.
* sysdeps/sparc/sparc32/elf/start.S: Likewise.

3
sysdeps/unix/sparc/sysdep.h
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@ -39,6 +39,9 @@ __sparc_get_pc_thunk.reg: \
.previous; \
.endif;
/* Even when v9 we use a call sequence instead of using "rd %pc" because
RDPC is extremely expensive and incurs a full pipeline flush. */
#define SETUP_PIC_REG(reg) \
SPARC_PIC_THUNK(reg) \
sethi %hi(_GLOBAL_OFFSET_TABLE_-4), %##reg; \