From f3ed8bfe8a82af1870ddc8696ed4cc1d5aa6b441 Mon Sep 17 00:00:00 2001 From: Rich Felker Date: Mon, 5 Aug 2019 18:41:47 -0400 Subject: fix x87 stack imbalance in corner cases of i386 math asm commit 31c5fb80b9eae86f801be4f46025bc6532a554c5 introduced underflow code paths for the i386 math asm, along with checks on the fpu status word to skip the underflow-generation instructions if the underflow flag was already raised. unfortunately, at least one such path, in log1p, returned with 2 items on the x87 stack rather than just 1 item for the return value. this is a violation of the ABI's calling convention, and could cause subsequent floating point code to produce NANs due to x87 stack overflow. if floating point results are used in flow control, this can lead to runaway wrong code execution. rather than reviewing each "underflow already raised" code path for correctness, remove them all. they're likely slower than just performing the underflow code unconditionally, and significantly more complex. all of this code should be ripped out and replaced by C source files with inline asm. doing so would preclude this kind of error by having the compiler perform all x87 stack register allocation and stack manipulation, and would produce comparable or better code. however such a change is a much larger project. --- src/math/i386/asin.s | 10 ++-------- src/math/i386/atan.s | 7 ++----- src/math/i386/atan2.s | 5 +---- src/math/i386/atan2f.s | 5 +---- src/math/i386/atanf.s | 7 ++----- src/math/i386/exp.s | 10 ++-------- src/math/i386/log1p.s | 7 ++----- src/math/i386/log1pf.s | 7 ++----- 8 files changed, 14 insertions(+), 44 deletions(-) diff --git a/src/math/i386/asin.s b/src/math/i386/asin.s index a9f691bf..920d967a 100644 --- a/src/math/i386/asin.s +++ b/src/math/i386/asin.s @@ -7,13 +7,10 @@ asinf: cmp $0x01000000,%eax jae 1f # subnormal x, return x with underflow - fnstsw %ax - and $16,%ax - jnz 2f fld %st(0) fmul %st(1) fstps 4(%esp) -2: ret + ret .global asinl .type asinl,@function @@ -30,11 +27,8 @@ asin: cmp $0x00200000,%eax jae 1f # subnormal x, return x with underflow - fnstsw %ax - and $16,%ax - jnz 2f fsts 4(%esp) -2: ret + ret 1: fld %st(0) fld1 fsub %st(0),%st(1) diff --git a/src/math/i386/atan.s b/src/math/i386/atan.s index d73137b2..a26feae1 100644 --- a/src/math/i386/atan.s +++ b/src/math/i386/atan.s @@ -10,8 +10,5 @@ atan: fpatan ret # subnormal x, return x with underflow -1: fnstsw %ax - and $16,%ax - jnz 2f - fsts 4(%esp) -2: ret +1: fsts 4(%esp) + ret diff --git a/src/math/i386/atan2.s b/src/math/i386/atan2.s index a7d2979b..1fa0524d 100644 --- a/src/math/i386/atan2.s +++ b/src/math/i386/atan2.s @@ -10,8 +10,5 @@ atan2: cmp $0x00200000,%eax jae 1f # subnormal x, return x with underflow - fnstsw %ax - and $16,%ax - jnz 1f fsts 4(%esp) -1: ret + ret diff --git a/src/math/i386/atan2f.s b/src/math/i386/atan2f.s index 14b88ce5..0b264726 100644 --- a/src/math/i386/atan2f.s +++ b/src/math/i386/atan2f.s @@ -10,10 +10,7 @@ atan2f: cmp $0x01000000,%eax jae 1f # subnormal x, return x with underflow - fnstsw %ax - and $16,%ax - jnz 1f fld %st(0) fmul %st(1) fstps 4(%esp) -1: ret + ret diff --git a/src/math/i386/atanf.s b/src/math/i386/atanf.s index 8caddefa..893beac5 100644 --- a/src/math/i386/atanf.s +++ b/src/math/i386/atanf.s @@ -10,10 +10,7 @@ atanf: fpatan ret # subnormal x, return x with underflow -1: fnstsw %ax - and $16,%ax - jnz 2f - fld %st(0) +1: fld %st(0) fmul %st(1) fstps 4(%esp) -2: ret + ret diff --git a/src/math/i386/exp.s b/src/math/i386/exp.s index c7aa5b6e..df87c497 100644 --- a/src/math/i386/exp.s +++ b/src/math/i386/exp.s @@ -7,13 +7,10 @@ expm1f: cmp $0x01000000,%eax jae 1f # subnormal x, return x with underflow - fnstsw %ax - and $16,%ax - jnz 2f fld %st(0) fmul %st(1) fstps 4(%esp) -2: ret + ret .global expm1l .type expm1l,@function @@ -30,11 +27,8 @@ expm1: cmp $0x00200000,%eax jae 1f # subnormal x, return x with underflow - fnstsw %ax - and $16,%ax - jnz 2f fsts 4(%esp) -2: ret + ret 1: fldl2e fmulp mov $0xc2820000,%eax diff --git a/src/math/i386/log1p.s b/src/math/i386/log1p.s index 6b6929c7..354f391a 100644 --- a/src/math/i386/log1p.s +++ b/src/math/i386/log1p.s @@ -16,9 +16,6 @@ log1p: fyl2x ret # subnormal x, return x with underflow -2: fnstsw %ax - and $16,%ax - jnz 1f - fsts 4(%esp) +2: fsts 4(%esp) fstp %st(1) -1: ret + ret diff --git a/src/math/i386/log1pf.s b/src/math/i386/log1pf.s index c0bcd30f..4d3484cd 100644 --- a/src/math/i386/log1pf.s +++ b/src/math/i386/log1pf.s @@ -16,10 +16,7 @@ log1pf: fyl2x ret # subnormal x, return x with underflow -2: fnstsw %ax - and $16,%ax - jnz 1f - fxch +2: fxch fmul %st(1) fstps 4(%esp) -1: ret + ret -- cgit v1.2.1