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Stash reent marker in upper bits of s1 on AMD GCN 

s[0:3] contain a descriptor used to set up the initial value of the
stack, but only the lower 48 bits of s[0:1] are currently used.
The reent marker is currently set in s3, but by stashing it in the
upper 16 bits of s[0:1] instead, s3 can be freed up for other purposes.
This commit is contained in:
Kwok Cheung Yeung 2019-11-07 14:46:41 -08:00 committed by Ken Brown
parent 2fd6bf96b9
commit 77c1a1e903
1 changed files with 10 additions and 10 deletions
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20
newlib/libc/machine/amdgcn/getreent.c
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@ -34,7 +34,7 @@ __getreent (void)
s11 contains the offset to the base of the stack.
s[4:5] contains the dispatch pointer.
WARNING: this code will break if s[0:3] is ever used for anything! */
WARNING: this code will break if s[0:1] is ever used for anything! */
const register unsigned long buffer_descriptor asm("s0");
unsigned long private_segment = buffer_descriptor & 0x0000ffffffffffff;
const register unsigned int stack_offset asm("s11");
@ -54,20 +54,20 @@ __getreent (void)
if (sp >= addr)
goto stackoverflow;
/* Place a marker in s3 to indicate that the reent data is initialized.
The register is known to hold part of an unused buffer descriptor
when the kernel is launched. This may not be unused forever, but
we already used s0 and s1 above, so this doesn't do extra harm. */
register int s3 asm("s3");
if (s3 != 123456)
/* Stash a marker in the unused upper 16 bits of s[0:1] to indicate that
the reent data is initialized. */
const register unsigned int s1 asm("s1");
unsigned int marker = s1 >> 16;
if (marker != 12345)
{
asm("s_mov_b32 s3, 123456");
data->marker = 123456;
asm("s_and_b32\ts1, s1, 0xffff");
asm("s_or_b32\ts1, s1, (12345 << 16)");
data->marker = 12345;
__builtin_memset (&data->reent, 0, sizeof(struct _reent));
_REENT_INIT_PTR_ZEROED (&data->reent);
}
else if (data->marker != 123456)
else if (data->marker != 12345)
goto stackoverflow;