I've come across an issue with using the -pg switch for profiling on the DJGPP DOS platform, using GCC 4.1.0. After some digging through disassembly, I found that the part of the function prologue for main() before the call to mcount() is using the ECX register, and the call to the mcount() function appears to be clobbering it. I've verified that GCC 4.1.0 for Linux appears to work, and GCC 4.0.1 for DJGPP also works fine.
Here's the assembly for the function prologue of main(): lea 0x4(%esp),%ecx and $0xfffffff0,%esp pushl 0xfffffffc(%ecx) push %ebp mov %esp,%ebp push %ebx push %ecx mov $0x146e0,%edx call 0x3890 <mcount> mov %ecx,%ebx <--- clobbered value of ECX is used And here's the relevant portion of mcount(): push %ebp mov %esp,%ebp push %edi push %esi push %ebx sub $0x1c,%esp mov %edx,0xffffffec(%ebp) mov 0x15ca0,%ecx <--- ECX gets clobbered So I'm trying to figure out what's changed; is there a new requirement that ECX is not preserved that didn't exist before? I've looked through some GCC source but I'm really not at all sure what I should be looking for. TIA...
