Hi Warren, Sorry, on list, but it may help the willing eyeballs if these two were made easily available, e.g. a pastebin like curl -sSF 'f:1=<-' ix.io <lib/fwrite.c as then spotting the cause of wouldn't involve downloads, make, etc., that make it easy to think one doesn't have the time to look. :-) -- Cheers, Ralph.

Hi Warren, I've always tried to avoid x86 and friends for ARM, so I may be wrong, but the run up to the first of the two memcpy() calls looks the same to me. Here's the assembler, values given an RBP of 100, and the stack contents. Good version first, bad second. rbp = 100 L29: movq -8(%rbp),%rax rax = *92 pushq %rax *92 movq 16(%rbp),%rax rax = *116 pushq %rax *92 *116 movq $64,%rax rax = 64 pushq %rax *92 *116 64 movq 32(%rbp),%rax rax = *132 popq %rcx rcx = 64 *92 *116 addq %rcx,%rax rcx = 64+*132 movq (%rax),%rax rax = *(64+*132) pushq %rax *92 *116 *(64+*132) movq $40,%rax rax = 40 pushq %rax *92 *116 *(64+*132) 40 movq 32(%rbp),%rax rax = *132 popq %rcx rcx = 40 *92 *116 *(64+*132) addq %rcx,%rax rax = 40+*132 movq (%rax),%rax rax = *(40+*132) popq %rcx rcx = *(64+*132) *92 *116 addq %rcx,%rax rax = *(64+*132)+*(40+*132) pushq %rax *92 *116 *(64+*132)+*(40+*132) call Cmemcpy rbp = 100 L29: movq -8(%rbp),%r8 r8 = *92 pushq %r8 *92 movq 16(%rbp),%r8 r8 = *116 pushq %r8 *92 *116 movq $64,%r8 r8 = 64 movq 32(%rbp),%r9 r9 = *132 addq %r9,%r8 r8 = *132+64 movq (%r8),%r8 r8 = *(*132+64) movq $40,%r9 r9 = 40 movq 32(%rbp),%r10 r10 = *132 addq %r10,%r9 r9 = *132+40 movq (%r9),%r9 r9 = *(*132+40) addq %r9,%r8 r8 = *(*132+64)+*(*132+40) pushq %r8 *92 *116 *(*132+64)+*(*132+40) call Cmemcpy A glance at the second memcpy() call look equivalent too. So perhaps it's not calculating the parameters to memcpy() that's wrong, but the inputs into those calculations being faulty? I'd use gdb(1) to break at particular instructions, examine memory, etc., to work backwards through the bad version until spotting where good data becomes bad. -- Cheers, Ralph.

I have all to much experience with back end bugs, usually when someone porting PCC asked for help. The advice I always gave first was:  "what would the correct output look like?" 90% of the time, they didn't know.  And it's hard to hit the target if you don't know where it is... Once you know what you want, then you figure out the first instruction that isn't right and hit it with everything you have... Hope this helps... Steve ----- Original Message ----- From: "Ralph Corderoy" &lt;ralph(a)inputplus.co.uk&gt; To:<tuhs@tuhs.org> Cc: Sent:Sun, 29 Sep 2019 11:50:16 +0100 Subject:Re: [TUHS] OT: compiler back-end bug Hi Warren, https://minnie.tuhs.org/wktcloud/index.php/s/HQjsggHb4i6wdWM?path=%2FSfiles I've always tried to avoid x86 and friends for ARM, so I may be wrong, but the run up to the first of the two memcpy() calls looks the same to me. Here's the assembler, values given an RBP of 100, and the stack contents. Good version first, bad second. rbp = 100 L29: movq -8(%rbp),%rax rax = *92 pushq %rax *92 movq 16(%rbp),%rax rax = *116 pushq %rax *92 *116 movq $64,%rax rax = 64 pushq %rax *92 *116 64 movq 32(%rbp),%rax rax = *132 popq %rcx rcx = 64 *92 *116 addq %rcx,%rax rcx = 64+*132 movq (%rax),%rax rax = *(64+*132) pushq %rax *92 *116 *(64+*132) movq $40,%rax rax = 40 pushq %rax *92 *116 *(64+*132) 40 movq 32(%rbp),%rax rax = *132 popq %rcx rcx = 40 *92 *116 *(64+*132) addq %rcx,%rax rax = 40+*132 movq (%rax),%rax rax = *(40+*132) popq %rcx rcx = *(64+*132) *92 *116 addq %rcx,%rax rax = *(64+*132)+*(40+*132) pushq %rax *92 *116 *(64+*132)+*(40+*132) call Cmemcpy rbp = 100 L29: movq -8(%rbp),%r8 r8 = *92 pushq %r8 *92 movq 16(%rbp),%r8 r8 = *116 pushq %r8 *92 *116 movq $64,%r8 r8 = 64 movq 32(%rbp),%r9 r9 = *132 addq %r9,%r8 r8 = *132+64 movq (%r8),%r8 r8 = *(*132+64) movq $40,%r9 r9 = 40 movq 32(%rbp),%r10 r10 = *132 addq %r10,%r9 r9 = *132+40 movq (%r9),%r9 r9 = *(*132+40) addq %r9,%r8 r8 = *(*132+64)+*(*132+40) pushq %r8 *92 *116 *(*132+64)+*(*132+40) call Cmemcpy A glance at the second memcpy() call look equivalent too. So perhaps it's not calculating the parameters to memcpy() that's wrong, but the inputs into those calculations being faulty? I'd use gdb(1) to break at particular instructions, examine memory, etc., to work backwards through the bad version until spotting where good data becomes bad. -- Cheers, Ralph.