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author | Bruno Haible <bruno@clisp.org> | 2023-10-24 08:37:16 -0300 |
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committer | Adhemerval Zanella <adhemerval.zanella@linaro.org> | 2023-12-19 15:12:38 -0300 |
commit | 787282dede7f134fdb22155cee0c35172e3e28f3 (patch) | |
tree | ef7d2a333bd0cf9118f1afd3183186db07ed0513 /sysdeps/x86_64 | |
parent | 47a9eeb9ba72fd30766bdf4faa7d46b8ca33a7fd (diff) | |
download | glibc-787282dede7f134fdb22155cee0c35172e3e28f3.tar.gz glibc-787282dede7f134fdb22155cee0c35172e3e28f3.tar.xz glibc-787282dede7f134fdb22155cee0c35172e3e28f3.zip |
x86: Do not raises floating-point exception traps on fesetexceptflag (BZ 30990)
According to ISO C23 (7.6.4.4), fesetexcept is supposed to set floating-point exception flags without raising a trap (unlike feraiseexcept, which is supposed to raise a trap if feenableexcept was called with the appropriate argument). The flags can be set in the 387 unit or in the SSE unit. When we need to clear a flag, we need to do so in both units, due to the way fetestexcept is implemented. When we need to set a flag, it is sufficient to do it in the SSE unit, because that is guaranteed to not trap. However, on i386 CPUs that have only a 387 unit, set the flags in the 387, as long as this cannot trap. Co-authored-by: Adhemerval Zanella <adhemerval.zanella@linaro.org> Reviewed-by: Carlos O'Donell <carlos@redhat.com>
Diffstat (limited to 'sysdeps/x86_64')
-rw-r--r-- | sysdeps/x86_64/fpu/fsetexcptflg.c | 24 |
1 files changed, 14 insertions, 10 deletions
diff --git a/sysdeps/x86_64/fpu/fsetexcptflg.c b/sysdeps/x86_64/fpu/fsetexcptflg.c index a3ac1dea01..2ce2b509f2 100644 --- a/sysdeps/x86_64/fpu/fsetexcptflg.c +++ b/sysdeps/x86_64/fpu/fsetexcptflg.c @@ -22,30 +22,34 @@ int fesetexceptflag (const fexcept_t *flagp, int excepts) { + /* The flags can be set in the 387 unit or in the SSE unit. + When we need to clear a flag, we need to do so in both units, + due to the way fetestexcept() is implemented. + When we need to set a flag, it is sufficient to do it in the SSE unit, + because that is guaranteed to not trap. */ + fenv_t temp; unsigned int mxcsr; - /* XXX: Do we really need to set both the exception in both units? - Shouldn't it be enough to set only the SSE unit? */ + excepts &= FE_ALL_EXCEPT; /* Get the current x87 FPU environment. We have to do this since we cannot separately set the status word. */ __asm__ ("fnstenv %0" : "=m" (*&temp)); - temp.__status_word &= ~(excepts & FE_ALL_EXCEPT); - temp.__status_word |= *flagp & excepts & FE_ALL_EXCEPT; + /* Clear relevant flags. */ + temp.__status_word &= ~(excepts & ~ *flagp); - /* Store the new status word (along with the rest of the environment. - Possibly new exceptions are set but they won't get executed unless - the next floating-point instruction. */ + /* Store the new status word (along with the rest of the environment). */ __asm__ ("fldenv %0" : : "m" (*&temp)); - /* And now the same for SSE. */ + /* And now similarly for SSE. */ __asm__ ("stmxcsr %0" : "=m" (*&mxcsr)); - mxcsr &= ~(excepts & FE_ALL_EXCEPT); - mxcsr |= *flagp & excepts & FE_ALL_EXCEPT; + /* Clear or set relevant flags. */ + mxcsr ^= (mxcsr ^ *flagp) & excepts; + /* Put the new data in effect. */ __asm__ ("ldmxcsr %0" : : "m" (*&mxcsr)); /* Success. */ |