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Groups > comp.lang.c++ > #68855
| From | scott@slp53.sl.home (Scott Lurndal) |
|---|---|
| Subject | Re: alloca()-support |
| Newsgroups | comp.lang.c++, comp.lang.c |
| References | (3 earlier) <qmtc2o$pmp$4@dont-email.me> <qmtc6v$uk5$1@news.albasani.net> <qmtfeh$gno$1@dont-email.me> <lRskF.22050$XA2.21391@fx05.iad> <qmuov1$n71$2@news.albasani.net> |
| Message-ID | <J7KkF.4573$KB2.3280@fx02.iad> (permalink) |
| Organization | UsenetServer - www.usenetserver.com |
| Date | 2019-10-01 15:19 +0000 |
Cross-posted to 2 groups.
Bonita Montero <Bonita.Montero@gmail.com> writes:
>> mov %rsp, %rax # rax now has starting address of alloca() region
>
>The compiler usually uses RPB to remember the frame-pointer-address
>at the prolog of the function. EBP is more suitable because it can
>be restored in one step by the x86 LEAVE-instruction.
So what? The RSP is restored automatically by the ret instruction.
int f(unsigned long len)
{
char *f = alloca(len);
for (int i=0; i < 0; i++) {
*f++ = '\0';
}
return 0;
}
gcc output:
0000000000400540 <f>:
#include <alloca.h>
#include <stdlib.h>
int f(unsigned long len)
{
400540: 55 push %rbp
400541: 48 89 e5 mov %rsp,%rbp
400544: 48 83 ec 20 sub $0x20,%rsp
400548: 48 89 7d e8 mov %rdi,-0x18(%rbp)
char *f = alloca(len);
40054c: 48 8b 45 e8 mov -0x18(%rbp),%rax
400550: 48 8d 50 0f lea 0xf(%rax),%rdx
400554: b8 10 00 00 00 mov $0x10,%eax
400559: 48 83 e8 01 sub $0x1,%rax
40055d: 48 01 d0 add %rdx,%rax
400560: b9 10 00 00 00 mov $0x10,%ecx
400565: ba 00 00 00 00 mov $0x0,%edx
40056a: 48 f7 f1 div %rcx
40056d: 48 6b c0 10 imul $0x10,%rax,%rax
400571: 48 29 c4 sub %rax,%rsp <===== Alloca(len)
400574: 48 89 e0 mov %rsp,%rax <===== Remember f in %rax
400577: 48 83 c0 0f add $0xf,%rax <===== Align it
40057b: 48 c1 e8 04 shr $0x4,%rax
40057f: 48 c1 e0 04 shl $0x4,%rax
400583: 48 89 45 f8 mov %rax,-0x8(%rbp) <== And save in stack frame
for (int i=0; i < 0; i++) {
400587: c7 45 f4 00 00 00 00 movl $0x0,-0xc(%rbp)
40058e: eb 13 jmp 4005a3 <f+0x63>
*f++ = '\0';
400590: 48 8b 45 f8 mov -0x8(%rbp),%rax
400594: 48 8d 50 01 lea 0x1(%rax),%rdx
400598: 48 89 55 f8 mov %rdx,-0x8(%rbp)
40059c: c6 00 00 movb $0x0,(%rax)
40059f: 83 45 f4 01 addl $0x1,-0xc(%rbp)
4005a3: 83 7d f4 00 cmpl $0x0,-0xc(%rbp)
4005a7: 78 e7 js 400590 <f+0x50>
*f++ = '\0';
}
return 0;
4005a9: b8 00 00 00 00 mov $0x0,%eax
}
4005ae: c9 leaveq
4005af: c3 retq
>
>> sub %rcx, %rsp # rcx is the number of bytes being allocated.
>> ....
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alloca()-support Bonita Montero <Bonita.Montero@gmail.com> - 2019-09-30 14:02 +0200
Re: alloca()-support Frederick Gotham <cauldwell.thomas@gmail.com> - 2019-09-30 07:02 -0700
Re: alloca()-support Bonita Montero <Bonita.Montero@gmail.com> - 2019-09-30 16:09 +0200
Re: alloca()-support Bo Persson <bo@bo-persson.se> - 2019-09-30 17:29 +0200
Re: alloca()-support Bonita Montero <Bonita.Montero@gmail.com> - 2019-09-30 17:33 +0200
Re: alloca()-support gazelle@shell.xmission.com (Kenny McCormack) - 2019-09-30 16:26 +0000
Re: alloca()-support Anton Shepelev <anton.txt@g{oogle}mail.com> - 2019-09-30 17:12 +0300
Re: alloca()-support Bonita Montero <Bonita.Montero@gmail.com> - 2019-09-30 16:16 +0200
Re: alloca()-support Anton Shepelev <anton.txt@g{oogle}mail.com> - 2019-09-30 17:30 +0300
Re: alloca()-support Bonita Montero <Bonita.Montero@gmail.com> - 2019-09-30 16:44 +0200
Re: alloca()-support Anton Shepelev <anton.txt@gmail.com> - 2019-10-02 00:36 +0300
Re: alloca()-support Bonita Montero <Bonita.Montero@gmail.com> - 2019-10-02 06:28 +0200
Re: alloca()-support Anton Shepelev <anton.txt@gmail.com> - 2019-10-02 16:08 +0300
Re: alloca()-support Bonita Montero <Bonita.Montero@gmail.com> - 2019-10-02 15:42 +0200
Re: alloca()-support scott@slp53.sl.home (Scott Lurndal) - 2019-09-30 14:30 +0000
Re: alloca()-support Anton Shepelev <anton.txt@g{oogle}mail.com> - 2019-09-30 17:33 +0300
Re: alloca()-support David Brown <david.brown@hesbynett.no> - 2019-09-30 16:56 +0200
Re: alloca()-support Melzzzzz <Melzzzzz@zzzzz.com> - 2019-09-30 15:29 +0000
Re: alloca()-support Bonita Montero <Bonita.Montero@gmail.com> - 2019-09-30 17:31 +0200
Re: alloca()-support Melzzzzz <Melzzzzz@zzzzz.com> - 2019-10-01 07:03 +0000
Re: alloca()-support Bonita Montero <Bonita.Montero@gmail.com> - 2019-10-01 10:57 +0200
Re: alloca()-support Melzzzzz <Melzzzzz@zzzzz.com> - 2019-10-01 18:49 +0000
Re: alloca()-support Bonita Montero <Bonita.Montero@gmail.com> - 2019-10-01 21:20 +0200
Re: alloca()-support scott@slp53.sl.home (Scott Lurndal) - 2019-10-01 20:39 +0000
Re: alloca()-support Melzzzzz <Melzzzzz@zzzzz.com> - 2019-10-02 04:15 +0000
Re: alloca()-support Bonita Montero <Bonita.Montero@gmail.com> - 2019-10-02 06:28 +0200
Re: alloca()-support Melzzzzz <Melzzzzz@zzzzz.com> - 2019-10-02 04:29 +0000
Re: alloca()-support Keith Thompson <kst-u@mib.org> - 2019-09-30 11:14 -0700
Re: alloca()-support Bonita Montero <Bonita.Montero@gmail.com> - 2019-09-30 18:04 +0200
Re: alloca()-support William Ahern <william@25thandClement.com> - 2019-09-30 11:01 -0700
Re: alloca()-support Bonita Montero <Bonita.Montero@gmail.com> - 2019-10-01 07:19 +0200
Re: alloca()-support Paavo Helde <myfirstname@osa.pri.ee> - 2019-09-30 22:26 +0300
Re: alloca()-support scott@slp53.sl.home (Scott Lurndal) - 2019-09-30 19:46 +0000
Re: alloca()-support Bonita Montero <Bonita.Montero@gmail.com> - 2019-10-01 07:32 +0200
Re: alloca()-support Paavo Helde <myfirstname@osa.pri.ee> - 2019-10-01 09:08 +0300
Re: alloca()-support Bonita Montero <Bonita.Montero@gmail.com> - 2019-10-01 08:35 +0200
Re: alloca()-support Soviet_Mario <SovietMario@CCCP.MIR> - 2019-09-30 18:48 +0200
Re: alloca()-support Bonita Montero <Bonita.Montero@gmail.com> - 2019-09-30 18:51 +0200
Re: alloca()-support Soviet_Mario <SovietMario@CCCP.MIR> - 2019-09-30 18:55 +0200
Re: alloca()-support Bonita Montero <Bonita.Montero@gmail.com> - 2019-09-30 18:58 +0200
Re: alloca()-support Soviet_Mario <SovietMario@CCCP.MIR> - 2019-09-30 19:53 +0200
Re: alloca()-support Keith Thompson <kst-u@mib.org> - 2019-09-30 11:13 -0700
Re: alloca()-support scott@slp53.sl.home (Scott Lurndal) - 2019-09-30 19:38 +0000
Re: alloca()-support Bonita Montero <Bonita.Montero@gmail.com> - 2019-10-01 07:41 +0200
Re: alloca()-support scott@slp53.sl.home (Scott Lurndal) - 2019-10-01 15:19 +0000
Re: alloca()-support Bonita Montero <Bonita.Montero@gmail.com> - 2019-10-01 17:31 +0200
Re: alloca()-support Melzzzzz <Melzzzzz@zzzzz.com> - 2019-10-01 18:58 +0000
Re: alloca()-support Bonita Montero <Bonita.Montero@gmail.com> - 2019-10-01 21:24 +0200
Re: alloca()-support Melzzzzz <Melzzzzz@zzzzz.com> - 2019-10-02 04:28 +0000
Re: alloca()-support Bonita Montero <Bonita.Montero@gmail.com> - 2019-10-02 06:30 +0200
Re: alloca()-support Melzzzzz <Melzzzzz@zzzzz.com> - 2019-10-02 04:36 +0000
Re: alloca()-support David Brown <david.brown@hesbynett.no> - 2019-10-02 10:01 +0200
Re: alloca()-support Melzzzzz <Melzzzzz@zzzzz.com> - 2019-10-02 04:42 +0000
Re: alloca()-support David Brown <david.brown@hesbynett.no> - 2019-10-02 10:10 +0200
Re: alloca()-support Mel <mel@zzzzz.com> - 2019-10-02 15:13 +0200
Re: alloca()-support David Brown <david.brown@hesbynett.no> - 2019-10-01 21:10 +0200
Re: alloca()-support Bonita Montero <Bonita.Montero@gmail.com> - 2019-10-01 21:25 +0200
Re: alloca()-support scott@slp53.sl.home (Scott Lurndal) - 2019-10-01 20:44 +0000
Re: alloca()-support David Brown <david.brown@hesbynett.no> - 2019-10-01 23:26 +0200
Re: alloca()-support Joe Pfeiffer <pfeiffer@cs.nmsu.edu> - 2019-10-01 21:08 -0600
Re: alloca()-support David Brown <david.brown@hesbynett.no> - 2019-10-02 10:19 +0200
Re: alloca()-support Bonita Montero <Bonita.Montero@gmail.com> - 2019-10-02 06:39 +0200
Re: alloca()-support David Brown <david.brown@hesbynett.no> - 2019-10-02 10:34 +0200
Re: alloca()-support Mel <mel@zzzzz.com> - 2019-10-02 15:14 +0200
Re: alloca()-support Mel <mel@zzzzz.com> - 2019-10-02 15:18 +0200
Re: alloca()-support Bonita Montero <Bonita.Montero@gmail.com> - 2019-10-02 15:21 +0200
Re: alloca()-support Melzzzzz <Melzzzzz@zzzzz.com> - 2019-10-03 04:09 +0000
Re: alloca()-support Bonita Montero <Bonita.Montero@gmail.com> - 2019-10-03 07:48 +0200
Re: alloca()-support Melzzzzz <Melzzzzz@zzzzz.com> - 2019-10-03 05:49 +0000
Re: alloca()-support Bonita Montero <Bonita.Montero@gmail.com> - 2019-10-03 07:52 +0200
Re: alloca()-support Melzzzzz <Melzzzzz@zzzzz.com> - 2019-10-03 06:46 +0000
Re: alloca()-support Bonita Montero <Bonita.Montero@gmail.com> - 2019-10-03 10:59 +0200
Re: alloca()-support Soviet_Mario <SovietMario@CCCP.MIR> - 2019-10-03 13:39 +0200
Re: alloca()-support scott@slp53.sl.home (Scott Lurndal) - 2019-10-03 13:23 +0000
Re: alloca()-support David Brown <david.brown@hesbynett.no> - 2019-10-03 15:38 +0200
Re: alloca()-support scott@slp53.sl.home (Scott Lurndal) - 2019-10-03 14:51 +0000
Re: alloca()-support David Brown <david.brown@hesbynett.no> - 2019-10-04 09:49 +0200
Re: alloca()-support Soviet_Mario <SovietMario@CCCP.MIR> - 2019-10-03 21:47 +0200
Re: alloca()-support David Brown <david.brown@hesbynett.no> - 2019-10-04 09:53 +0200
Re: alloca()-support Soviet_Mario <SovietMario@CCCP.MIR> - 2019-10-03 21:52 +0200
Re: alloca()-support Bonita Montero <Bonita.Montero@gmail.com> - 2019-10-01 07:39 +0200
Re: alloca()-support James Kuyper <jameskuyper@alumni.caltech.edu> - 2019-09-30 21:36 -0400
Re: alloca()-support Philipp Klaus Krause <pkk@spth.de> - 2019-09-30 19:14 +0200
Re: alloca()-support Bonita Montero <Bonita.Montero@gmail.com> - 2019-09-30 19:16 +0200
Re: alloca()-support Robert Wessel <robertwessel2@yahoo.com> - 2019-10-01 00:18 -0500
Re: alloca()-support Bonita Montero <Bonita.Montero@gmail.com> - 2019-10-01 07:43 +0200
Re: alloca()-support Keith Thompson <kst-u@mib.org> - 2019-10-01 02:42 -0700
Re: alloca()-support James Kuyper <jameskuyper@alumni.caltech.edu> - 2019-10-01 08:11 -0400
Re: alloca()-support Bonita Montero <Bonita.Montero@gmail.com> - 2019-10-01 14:53 +0200
Re: alloca()-support scott@slp53.sl.home (Scott Lurndal) - 2019-09-30 17:52 +0000
Re: alloca()-support Joe Pfeiffer <pfeiffer@cs.nmsu.edu> - 2019-09-30 11:20 -0600
Re: alloca()-support Bonita Montero <Bonita.Montero@gmail.com> - 2019-09-30 19:42 +0200
Re: alloca()-support Soviet_Mario <SovietMario@CCCP.MIR> - 2019-09-30 20:02 +0200
Re: alloca()-support Soviet_Mario <SovietMario@CCCP.MIR> - 2019-09-30 19:54 +0200
Re: alloca()-support Joe Pfeiffer <pfeiffer@cs.nmsu.edu> - 2019-09-30 14:28 -0600
Re: alloca()-support David Brown <david.brown@hesbynett.no> - 2019-10-01 09:38 +0200
Re: alloca()-support Soviet_Mario <SovietMario@CCCP.MIR> - 2019-09-30 20:01 +0200
Re: alloca()-support Manfred <noname@add.invalid> - 2019-10-01 17:45 +0200
Re: alloca()-support Frederick Gotham <cauldwell.thomas@gmail.com> - 2019-10-02 00:03 -0700
Re: alloca()-support Paavo Helde <myfirstname@osa.pri.ee> - 2019-10-02 11:30 +0300
Re: alloca()-support Ian Collins <ian-news@hotmail.com> - 2019-10-02 21:34 +1300
Re: alloca()-support Frederick Gotham <cauldwell.thomas@gmail.com> - 2019-10-02 01:36 -0700
Re: alloca()-support Ian Collins <ian-news@hotmail.com> - 2019-10-02 21:41 +1300
Re: alloca()-support Frederick Gotham <cauldwell.thomas@gmail.com> - 2019-10-02 02:28 -0700
Re: alloca()-support "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2019-10-02 02:35 -0700
Re: alloca()-support Frederick Gotham <cauldwell.thomas@gmail.com> - 2019-10-02 02:43 -0700
Re: alloca()-support Anton Shepelev <anton.txt@gmail.com> - 2019-10-02 16:26 +0300
Re: alloca()-support "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2019-10-02 12:33 -0700
Re: alloca()-support Anton Shepelev <anton.txt@gmail.com> - 2019-10-03 01:47 +0300
Re: alloca()-support "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2019-10-05 14:08 -0700
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