http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50289
Bug #: 50289 Summary: [avr]: call-prologues saveing/restoring global register variables Classification: Unclassified Product: gcc Version: 4.6.1 Status: UNCONFIRMED Keywords: wrong-code Severity: normal Priority: P3 Component: target AssignedTo: unassig...@gcc.gnu.org ReportedBy: g...@gcc.gnu.org CC: eric.wedding...@atmel.com Target: avr void bar (long long, long long, void*); register char x asm ("7"); void foo (char a) { asm volatile ("":::"6"); bar (0, 0, &a); } This small program, compiles with avr-gcc-4.6.1 -mcall-prologues -S -Os -mmcu=atmega8 to foo: ldi r26,lo8(1) ldi r27,hi8(1) ldi r30,lo8(gs(1f)) ldi r31,hi8(gs(1f)) jmp __prologue_saves__+((18 - 13) * 2) 1: This means that __prologue_saves__ from libgcc saves R7 (i.e. R6..R17 and Y) even though R7 is a global register variable and must not saved/restored by function prologue/epilogue. The function to fix is avr.c:sequent_regs_live()