Messages in this thread Patch in this message |  | | Date | Thu, 29 Nov 2001 09:07:08 -0500 (EST) | From | "Richard B. Johnson" <> | Subject | Re: Compilation problem in ndisc.c / 2.5.1-pre2 : possible gcc bug? |
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On Wed, 28 Nov 2001, Brian Gerst wrote:
> "Richard B. Johnson" wrote: > > > > On Wed, 28 Nov 2001, Martin Eriksson wrote: > > > > > ----- Original Message ----- > > > From: "Richard B. Johnson" <root@chaos.analogic.com> > > > To: <erik@hensema.net> > > > Cc: <linux-kernel@vger.kernel.org> > > > Sent: Wednesday, November 28, 2001 8:09 PM > > > Subject: Re: Compilation problem in ndisc.c / 2.5.1-pre2 : possible gcc bug? > > > > > > > > > > On 28 Nov 2001, Erik Hensema wrote: > > > > > > > > > > > > > > I've been looking into the compile problems of net/ipv6/ndisc.c in > > > > > 2.5.1-pre2 and I found that the asm generated by gcc (2.95.3) is wrong: > > > > > > > > > > This is a small part of a diff betweem two asm files generated by gcc, > > > note > > > > > the missing \n's in the wrong code: > > > > > > > > > > - > > > > > - addl 0(%ebp), %edx > > > > > - adcl 4(%ebp), %edx > > > > > - adcl 8(%ebp), %edx > > > > > - adcl 12(%ebp), %edx > > > > > - adcl 0(%ecx), %edx > > > > > - adcl 4(%ecx), %edx > > > > > - adcl 8(%ecx), %edx > > > > > - adcl 12(%ecx), %edx > > > > > - adcl %edi, %edx > > > > > - adcl %eax, %edx > > > > > - adcl $0, %edx > > > > > - > > > > > + addl 0(%ebp), %edxadcl 4(%ebp), %edxadcl 8(%ebp), %edxadcl 12(%ebp), > > > %edxadcl 0(%ecx), %edxadcl 4(%ecx), %edxadcl 8(%ecx), %edxadcl 12(%ecx), > > > %edxadcl %edi, %edxadcl %eax, %edxadcl $0, %edx > > > > > > > > > > > > This is probably just some loop unrolling, not some as you say "wrong > > > > code". > > > > > > Correct me if I'm wrong, but I don't think "%edxadcl" really assembles.... > > > > No, but an edited 'diff' of the assembly output of a 'C' compiler doesn't > > really tell much. Note, no line numbers, no clue as to what the diff > > was about. The actual defective section of code would be much more > > instructive. For instance, is this as a result of an in-line macro > > expansion; the result of a <CR><LF> 'dos' file; the true output of > > a 'C' file with no __inline__ __asm__? > > It's from include/asm-i386/checksum.h, specifically csum_ipv6_magic(). > The asm statements in this header file need semicolons or explicit > newlines after each opcode. >
Yes. It isn't a 'C' compiler problem. Here is a patch. I remember some comment about "multi-line string literals are depreciated..." as a diagnostic message from some 'C' compiler version. Somebody should check this out. This patch is "for the way we used to do it..."
SNIP --- /usr/src/linux/include/asm-i386/checksum.h Tue Feb 1 02:41:14 2000 +++ checksum.h Thu Nov 29 08:56:11 2001 @@ -69,25 +69,24 @@ unsigned int ihl) { unsigned int sum; - __asm__ __volatile__(" - movl (%1), %0 - subl $4, %2 - jbe 2f - addl 4(%1), %0 - adcl 8(%1), %0 - adcl 12(%1), %0 -1: adcl 16(%1), %0 - lea 4(%1), %1 - decl %2 - jne 1b - adcl $0, %0 - movl %0, %2 - shrl $16, %0 - addw %w2, %w0 - adcl $0, %0 - notl %0 -2: - " + __asm__ __volatile__( + "\n\tmovl (%1), %0\n" + "\tsubl $4, %2\n" + "\tjbe 2f\n" + "\taddl 4(%1), %0\n" + "\tadcl 8(%1), %0\n" + "\tadcl 12(%1), %0\n" + "1:\tadcl 16(%1), %0\n" + "\tlea 4(%1), %1\n" + "\tdecl %2\n" + "\tjne 1b\n" + "\tadcl $0, %0\n" + "\tmovl %0, %2\n" + "\tshrl $16, %0\n" + "\taddw %w2, %w0\n" + "\tadcl $0, %0\n" + "\tnotl %0\n" + "2:\n" /* Since the input registers which are loaded with iph and ipl are modified, we must also specify them as outputs, or gcc will assume they contain their original values. */ @@ -102,10 +101,9 @@ static inline unsigned int csum_fold(unsigned int sum) { - __asm__(" - addl %1, %0 - adcl $0xffff, %0 - " + __asm__( + "\n\taddl %1, %0\n" + "\tadcl $0xffff, %0\n" : "=r" (sum) : "r" (sum << 16), "0" (sum & 0xffff0000) ); @@ -118,12 +116,11 @@ unsigned short proto, unsigned int sum) { - __asm__(" - addl %1, %0 - adcl %2, %0 - adcl %3, %0 - adcl $0, %0 - " + __asm__( + "\n\taddl %1, %0\n" + "\tadcl %2, %0\n" + "\tadcl %3, %0\n" + "\tadcl $0, %0\n" : "=r" (sum) : "g" (daddr), "g"(saddr), "g"((ntohs(len)<<16)+proto*256), "0"(sum)); return sum; @@ -158,19 +155,18 @@ unsigned short proto, unsigned int sum) { - __asm__(" - addl 0(%1), %0 - adcl 4(%1), %0 - adcl 8(%1), %0 - adcl 12(%1), %0 - adcl 0(%2), %0 - adcl 4(%2), %0 - adcl 8(%2), %0 - adcl 12(%2), %0 - adcl %3, %0 - adcl %4, %0 - adcl $0, %0 - " + __asm__( + "\n\taddl 0(%1), %0\n" + "\tadcl 4(%1), %0\n" + "\tadcl 8(%1), %0\n" + "\tadcl 12(%1), %0\n" + "\tadcl 0(%2), %0\n" + "\tadcl 4(%2), %0\n" + "\tadcl 8(%2), %0\n" + "\tadcl 12(%2), %0\n" + "\tadcl %3, %0\n" + "\tadcl %4, %0\n" + "\tadcl $0, %0\n" : "=&r" (sum) : "r" (saddr), "r" (daddr), "r"(htonl(len)), "r"(htonl(proto)), "0"(sum)); SNIP
Here is something to test it with:
#define asmlinkage #define NULL (void *)0 #define DUMMY 0 #define VERIFY_WRITE DUMMY #define EFAULT DUMMY typedef unsigned int __u32; struct in6_addr{ int dummy; }; #include "checksum.h" void foo() { char bar[0x100]; ip_fast_csum(bar, sizeof(bar)); csum_ipv6_magic(NULL, NULL, sizeof(bar), DUMMY, DUMMY); csum_tcpudp_nofold(DUMMY, DUMMY, sizeof(bar), DUMMY, DUMMY); csum_fold(DUMMY); }
Just do `gcc -S -o xxx xxx.c` to see the code generated and verify that the stuborn 'C' compilers like these strings okay.
Cheers, Dick Johnson
Penguin : Linux version 2.4.1 on an i686 machine (799.53 BogoMips).
I was going to compile a list of innovations that could be attributed to Microsoft. Once I realized that Ctrl-Alt-Del was handled in the BIOS, I found that there aren't any.
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