+From f3ed8bfe8a82af1870ddc8696ed4cc1d5aa6b441 Mon Sep 17 00:00:00 2001
+From: Rich Felker <dalias@aerifal.cx>
+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(-)
+
+--- 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)
+--- 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
+--- 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
+--- 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
+--- 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
+--- 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
+--- 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
+--- 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
projects / openwrt / staging / dedeckeh.git / blobdiff