Thanks for your help, Richard! On Thu, Oct 17, 2019 at 03:55:31PM +0100, Richard Earnshaw (lists) wrote: > On 17/10/2019 15:04, Josef Wolf wrote: > >On Thu, Oct 17, 2019 at 02:37:11PM +0200, Matthias Pfaller wrote: > >>Why is the stack pointer so low at this point of execution? Using > >>0x20018000-0x20017d20 == 0x2e0 bytes of stack seems a little excessive > >>for just one call. > > > >Ah!... Looks like you've spotted the problem! Actually, the SP is decremented > >on every cycle of the loop: > > > > (gdb) disass > > Dump of assembler code for function memset: > > 0x08001008 <+0>: push {r4, lr} > > 0x0800100a <+2>: mov r4, r0 > > 0x0800100c <+4>: cbz r2, 0x8001014 <memset+12> > > => 0x0800100e <+6>: uxtb r1, r1 > > 0x08001010 <+8>: bl 0x8001008 <memset> > > 0x08001014 <+12>: mov r0, r4 > > 0x08001016 <+14>: pop {r4, pc} > > End of assembler dump. > > > >This looks REALLY suspicous to me. Every cycle of the loop in memset() is > >pushing something onto the stack?!? > > > >Without the -ftree-loop-distribute-patterns option, the memset() function > >looks entirely different: > > > > cbz r2, <memset+18> > > add r2, r0 > > subs r2, #1 > > uxtb r1, r1 > > subs r3, r0, #1 > > <+10>: strb.w r1, [r3, #1]! > > cmp r3, r2 > > bne.n <memset+10> > > <+18>: bx lr > > The compiler has spotted that you've written something that acts like memset > and optimized it into a function call to memset. So now you're recursing to > oblivion. Try adding -fno-builtin-memset to your compile options. This sounds reasonable, and I was actually thinking it would solve the problem. Unfortunately, -fno-built-memset doesn't have any effect. The same code is generated. -- Josef Wolf jw@xxxxxxxxxxxxx