Re: [fpc-devel] Question about NOP instructions
I figured that was the case. I don't intend to touch NOP instructions because of their uses in exception handling, but is there any harm in moving the local jumps to branch to after the NOP instructions, for example? Gareth aka. Kit On 03/11/2019 19:26, Florian Klämpfl wrote: Am 03.11.19 um 18:10 schrieb J. Gareth Moreton: Here's a larger snippet of the code in question - it's a bit too long to post, but there's a lot of conditional jumps to .Lj1859 earlier on: .Lj1875: testl $1024,92(%rbx) jne .Lj1878 leaq .Ld523(%rip),%rax movq %rax,-56(%rbp) movq $11,-64(%rbp) movq 64(%rbx),%rax movq %rax,-40(%rbp) movq $11,-48(%rbp) leaq .Ld524(%rip),%rax movq %rax,-24(%rbp) movq $11,-32(%rbp) movq 80(%rbx),%rcx leaq -72(%rbp),%rdx call CUSTOMCODETOOL$_$TCUSTOMCODETOOL_$__$$_MAINFILENAME$$ANSISTRING movq -72(%rbp),%rax movq %rax,-8(%rbp) movq $11,-16(%rbp) leaq -64(%rbp),%rcx movl $3,%edx call FILEPROCS_$$_DEBUGLN$array_of_const orl $1024,92(%rbx) .Lj1878: movq $0,24(%rbx) .Lj1859: nop .Lj1858: movq %rbp,%rcx call IDENTCOMPLETIONTOOL$_$TIDENTIFIERLISTITEM_$_GETNODE$$TCODETREENODE_$$_fin$0239 movq %rsi,%rax movq -88(%rbp),%rbx movq -80(%rbp),%rsi leaq (%rbp),%rsp popq %rbp ret .seh_handler __FPC_specific_handler,@unwind .seh_handlerdata .long 1 .long 0 .rva .Lj1857 .rva .Lj1858 .rva IDENTCOMPLETIONTOOL$_$TIDENTIFIERLISTITEM_$_GETNODE$$TCODETREENODE_$$_fin$0239 The two unwind entries (.rva) are labels that come right after a NOP instruction, and are the only references to these labels - meanwhile, the conditional jumps nearer the top go to the labels that appear before the nop instruction and are otherwise just testing registers and memory locations with no calls to other routines. Yes, this is exception handling code, have a look at compiler/x86_64/nx64flw.pas for details. ___ fpc-devel maillist - fpc-devel@lists.freepascal.org https://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-devel -- This email has been checked for viruses by Avast antivirus software. https://www.avast.com/antivirus ___ fpc-devel maillist - fpc-devel@lists.freepascal.org https://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-devel
Re: [fpc-devel] Question about NOP instructions
Am 03.11.19 um 18:10 schrieb J. Gareth Moreton: Here's a larger snippet of the code in question - it's a bit too long to post, but there's a lot of conditional jumps to .Lj1859 earlier on: .Lj1875: testl $1024,92(%rbx) jne .Lj1878 leaq .Ld523(%rip),%rax movq %rax,-56(%rbp) movq $11,-64(%rbp) movq 64(%rbx),%rax movq %rax,-40(%rbp) movq $11,-48(%rbp) leaq .Ld524(%rip),%rax movq %rax,-24(%rbp) movq $11,-32(%rbp) movq 80(%rbx),%rcx leaq -72(%rbp),%rdx call CUSTOMCODETOOL$_$TCUSTOMCODETOOL_$__$$_MAINFILENAME$$ANSISTRING movq -72(%rbp),%rax movq %rax,-8(%rbp) movq $11,-16(%rbp) leaq -64(%rbp),%rcx movl $3,%edx call FILEPROCS_$$_DEBUGLN$array_of_const orl $1024,92(%rbx) .Lj1878: movq $0,24(%rbx) .Lj1859: nop .Lj1858: movq %rbp,%rcx call IDENTCOMPLETIONTOOL$_$TIDENTIFIERLISTITEM_$_GETNODE$$TCODETREENODE_$$_fin$0239 movq %rsi,%rax movq -88(%rbp),%rbx movq -80(%rbp),%rsi leaq (%rbp),%rsp popq %rbp ret .seh_handler __FPC_specific_handler,@unwind .seh_handlerdata .long 1 .long 0 .rva .Lj1857 .rva .Lj1858 .rva IDENTCOMPLETIONTOOL$_$TIDENTIFIERLISTITEM_$_GETNODE$$TCODETREENODE_$$_fin$0239 The two unwind entries (.rva) are labels that come right after a NOP instruction, and are the only references to these labels - meanwhile, the conditional jumps nearer the top go to the labels that appear before the nop instruction and are otherwise just testing registers and memory locations with no calls to other routines. Yes, this is exception handling code, have a look at compiler/x86_64/nx64flw.pas for details. ___ fpc-devel maillist - fpc-devel@lists.freepascal.org https://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-devel
Re: [fpc-devel] Question about NOP instructions
Here's a larger snippet of the code in question - it's a bit too long to post, but there's a lot of conditional jumps to .Lj1859 earlier on: .Lj1875: testl $1024,92(%rbx) jne .Lj1878 leaq .Ld523(%rip),%rax movq %rax,-56(%rbp) movq $11,-64(%rbp) movq 64(%rbx),%rax movq %rax,-40(%rbp) movq $11,-48(%rbp) leaq .Ld524(%rip),%rax movq %rax,-24(%rbp) movq $11,-32(%rbp) movq 80(%rbx),%rcx leaq -72(%rbp),%rdx call CUSTOMCODETOOL$_$TCUSTOMCODETOOL_$__$$_MAINFILENAME$$ANSISTRING movq -72(%rbp),%rax movq %rax,-8(%rbp) movq $11,-16(%rbp) leaq -64(%rbp),%rcx movl $3,%edx call FILEPROCS_$$_DEBUGLN$array_of_const orl $1024,92(%rbx) .Lj1878: movq $0,24(%rbx) .Lj1859: nop .Lj1858: movq %rbp,%rcx call IDENTCOMPLETIONTOOL$_$TIDENTIFIERLISTITEM_$_GETNODE$$TCODETREENODE_$$_fin$0239 movq %rsi,%rax movq -88(%rbp),%rbx movq -80(%rbp),%rsi leaq (%rbp),%rsp popq %rbp ret .seh_handler __FPC_specific_handler,@unwind .seh_handlerdata .long 1 .long 0 .rva .Lj1857 .rva .Lj1858 .rva IDENTCOMPLETIONTOOL$_$TIDENTIFIERLISTITEM_$_GETNODE$$TCODETREENODE_$$_fin$0239 The two unwind entries (.rva) are labels that come right after a NOP instruction, and are the only references to these labels - meanwhile, the conditional jumps nearer the top go to the labels that appear before the nop instruction and are otherwise just testing registers and memory locations with no calls to other routines. In the meantime, I've got my jump code fully tested for i386-win32 and x86_64-win64, but am still documenting everything before I post them in a patch. I'm not sure how it behaves on non-Intel platforms yet, but I can confirm that it at least compiles. Gareth aka. Kit On 03/11/2019 10:44, Florian Klaempfl wrote: Am 02.11.2019 um 15:08 schrieb J. Gareth Moreton: Hi everyone, During my optimisation travels, I frequently stumble across lone NOP instructions in the compiled assembly language. Normally I leave these alone, but occasionally I stumble across things like this: ... movq $0,24(%rbx) .Lj1859: nop .Lj1858: movq %rbp,%rcx ... Can you please post the complete code? Without it, it's hard to say And there are jumps elsewhere that go to one label or the other. Is there any reason why a jump should lead to the NOP, or can they all be redirected to after the NOP instruction? Some are the result of exception handling on x86_64-win64, see compiler/x86_64/nx64flw.pas ___ fpc-devel maillist - fpc-devel@lists.freepascal.org https://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-devel -- This email has been checked for viruses by Avast antivirus software. https://www.avast.com/antivirus ___ fpc-devel maillist - fpc-devel@lists.freepascal.org https://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-devel
Re: [fpc-devel] Question about NOP instructions
Am 02.11.2019 um 15:08 schrieb J. Gareth Moreton: > Hi everyone, > > During my optimisation travels, I frequently stumble across lone NOP > instructions in the compiled assembly language. Normally I leave these > alone, but occasionally I stumble across things like this: > > ... > movq $0,24(%rbx) > .Lj1859: > nop > .Lj1858: > movq %rbp,%rcx > ... > Can you please post the complete code? Without it, it's hard to say > And there are jumps elsewhere that go to one label or the other. Is > there any reason why a jump should lead to the NOP, or can they all be > redirected to after the NOP instruction? Some are the result of exception handling on x86_64-win64, see compiler/x86_64/nx64flw.pas ___ fpc-devel maillist - fpc-devel@lists.freepascal.org https://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-devel
