diff options
Diffstat (limited to 'arch/arm/kernel/entry-common.S')
| -rw-r--r-- | arch/arm/kernel/entry-common.S | 124 |
1 files changed, 80 insertions, 44 deletions
diff --git a/arch/arm/kernel/entry-common.S b/arch/arm/kernel/entry-common.S index 2c1db77d784..f05a35a5969 100644 --- a/arch/arm/kernel/entry-common.S +++ b/arch/arm/kernel/entry-common.S @@ -92,75 +92,111 @@ ENDPROC(ret_from_fork) #define CALL(x) .long x #ifdef CONFIG_FUNCTION_TRACER +/* + * When compiling with -pg, gcc inserts a call to the mcount routine at the + * start of every function. In mcount, apart from the function's address (in + * lr), we need to get hold of the function's caller's address. + * + * Older GCCs (pre-4.4) inserted a call to a routine called mcount like this: + * + * bl mcount + * + * These versions have the limitation that in order for the mcount routine to + * be able to determine the function's caller's address, an APCS-style frame + * pointer (which is set up with something like the code below) is required. + * + * mov ip, sp + * push {fp, ip, lr, pc} + * sub fp, ip, #4 + * + * With EABI, these frame pointers are not available unless -mapcs-frame is + * specified, and if building as Thumb-2, not even then. + * + * Newer GCCs (4.4+) solve this problem by introducing a new version of mcount, + * with call sites like: + * + * push {lr} + * bl __gnu_mcount_nc + * + * With these compilers, frame pointers are not necessary. + * + * mcount can be thought of as a function called in the middle of a subroutine + * call. As such, it needs to be transparent for both the caller and the + * callee: the original lr needs to be restored when leaving mcount, and no + * registers should be clobbered. (In the __gnu_mcount_nc implementation, we + * clobber the ip register. This is OK because the ARM calling convention + * allows it to be clobbered in subroutines and doesn't use it to hold + * parameters.) + */ #ifdef CONFIG_DYNAMIC_FTRACE ENTRY(mcount) - stmdb sp!, {r0-r3, lr} - mov r0, lr - sub r0, r0, #MCOUNT_INSN_SIZE + stmdb sp!, {r0-r3, lr} + mov r0, lr + sub r0, r0, #MCOUNT_INSN_SIZE .globl mcount_call mcount_call: - bl ftrace_stub - ldr lr, [fp, #-4] @ restore lr - ldmia sp!, {r0-r3, pc} + bl ftrace_stub + ldr lr, [fp, #-4] @ restore lr + ldmia sp!, {r0-r3, pc} ENTRY(ftrace_caller) - stmdb sp!, {r0-r3, lr} - ldr r1, [fp, #-4] - mov r0, lr - sub r0, r0, #MCOUNT_INSN_SIZE + stmdb sp!, {r0-r3, lr} + ldr r1, [fp, #-4] + mov r0, lr + sub r0, r0, #MCOUNT_INSN_SIZE .globl ftrace_call ftrace_call: - bl ftrace_stub - ldr lr, [fp, #-4] @ restore lr - ldmia sp!, {r0-r3, pc} + bl ftrace_stub + ldr lr, [fp, #-4] @ restore lr + ldmia sp!, {r0-r3, pc} #else ENTRY(__gnu_mcount_nc) - stmdb sp!, {r0-r3, lr} - ldr r0, =ftrace_trace_function - ldr r2, [r0] - adr r0, ftrace_stub - cmp r0, r2 - bne gnu_trace - ldmia sp!, {r0-r3, ip, lr} - mov pc, ip + stmdb sp!, {r0-r3, lr} + ldr r0, =ftrace_trace_function + ldr r2, [r0] + adr r0, ftrace_stub + cmp r0, r2 + bne gnu_trace + ldmia sp!, {r0-r3, ip, lr} + mov pc, ip gnu_trace: - ldr r1, [sp, #20] @ lr of instrumented routine - mov r0, lr - sub r0, r0, #MCOUNT_INSN_SIZE - mov lr, pc - mov pc, r2 - ldmia sp!, {r0-r3, ip, lr} - mov pc, ip + ldr r1, [sp, #20] @ lr of instrumented routine + mov r0, lr + sub r0, r0, #MCOUNT_INSN_SIZE + mov lr, pc + mov pc, r2 + ldmia sp!, {r0-r3, ip, lr} + mov pc, ip ENTRY(mcount) - stmdb sp!, {r0-r3, lr} - ldr r0, =ftrace_trace_function - ldr r2, [r0] - adr r0, ftrace_stub - cmp r0, r2 - bne trace - ldr lr, [fp, #-4] @ restore lr - ldmia sp!, {r0-r3, pc} + stmdb sp!, {r0-r3, lr} + ldr r0, =ftrace_trace_function + ldr r2, [r0] + adr r0, ftrace_stub + cmp r0, r2 + bne trace + ldr lr, [fp, #-4] @ restore lr + ldmia sp!, {r0-r3, pc} trace: - ldr r1, [fp, #-4] @ lr of instrumented routine - mov r0, lr - sub r0, r0, #MCOUNT_INSN_SIZE - mov lr, pc - mov pc, r2 - ldr lr, [fp, #-4] @ restore lr - ldmia sp!, {r0-r3, pc} + ldr r1, [fp, #-4] @ lr of instrumented routine + mov r0, lr + sub r0, r0, #MCOUNT_INSN_SIZE + mov lr, pc + mov pc, r2 + ldr lr, [fp, #-4] @ restore lr + ldmia sp!, {r0-r3, pc} #endif /* CONFIG_DYNAMIC_FTRACE */ .globl ftrace_stub ftrace_stub: - mov pc, lr + mov pc, lr #endif /* CONFIG_FUNCTION_TRACER */ |