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Subject: Re: cpp /usr/include/threads.h fails; modfl segfaults
To: cygwin AT cygwin DOT com
References: <02b16d2e-9d51-de58-807b-3b31b2565b59 DOT ref AT aol DOT com>
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From: Brian Inglis <Brian DOT Inglis AT SystematicSw DOT ab DOT ca>
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Date: Sun, 30 Aug 2020 14:39:31 -0600
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On 2020-08-30 07:00, Corinna Vinschen wrote:
> On Aug 29 08:52, airplanemath via Cygwin wrote:
>> I have two reports.  A brief description of the system:
>> $ uname -a | sed "s/${HOSTNAME}/\${HOSTNAME}/g"
>> CYGWIN_NT-10.0 ${HOSTNAME} 3.1.7(0.340/5/3) 2020-08-22 17:48 x86_64 Cygwin
...
>> $ cat test.c
>> #include <math.h>
>> #include <stdio.h>
>> #include <stdlib.h>
>>
>> int main(int argc, char *argv[]) {
>>   long double a, b, c;
>>   char *num_end = NULL;
>>   a = b = c = 0.0L;
>>   if (argc != 2) {
>>     fprintf(stderr, "Usage: %s NUMBER\n", argv[0]);
>>     exit(1);
>>   }
>>   a = strtold(argv[1], &num_end);
>>   b = modfl(a, &c);
>>   printf("%Lf %Lf %Lf\n", a, b, c);
>>   return 0;
>> }
> 
> This is a bug in the assembler code taken from Mingw-w64.  The bug has
> been fixed upstream, so I just pulled in the upstream fixes.

The 64 bit fix doesn't pop eax but *now* flags eax as clobbered, whereas the 32
bit fix both pops and *now* flags eax as clobbered, which it really doesn't need
to do. Is this inconsistent treatment correct?

diff --git a/winsup/cygwin/math/modfl.c b/winsup/cygwin/math/modfl.c
index af75a8b..ef1ab16 100644 (file)
--- a/winsup/cygwin/math/modfl.c
+++ b/winsup/cygwin/math/modfl.c
@@ -21,7 +21,7 @@ modfl (long double value, long double* iptr)
     "fldcw (%%rsp)\n"
     "frndint\n"
     "fldcw 4(%%rsp)\n"
-    "addq $8, %%rsp\n" : "=t" (int_part) : "0" (value)); /* round */
+    "addq $8, %%rsp\n" : "=t" (int_part) : "0" (value) : "eax"); /* round */
 #elif defined(_X86_) || defined(__i386__)
   asm ("push %%eax\n\tsubl $8, %%esp\n"
     "fnstcw 4(%%esp)\n"
@@ -31,7 +31,7 @@ modfl (long double value, long double* iptr)
     "fldcw (%%esp)\n"
     "frndint\n"
     "fldcw 4(%%esp)\n"
-    "addl $8, %%esp\n\tpop %%eax\n" : "=t" (int_part) : "0" (value)); /* round */
+    "addl $8, %%esp\n\tpop %%eax\n" : "=t" (int_part) : "0" (value) : "eax");
/* round */
 #else
   int_part = truncl(value);
 #endif

-- 
Take care. Thanks, Brian Inglis, Calgary, Alberta, Canada

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