From 22f975f4ffa707ea24507f6899bb9f5a1ff034bc Mon Sep 17 00:00:00 2001 From: Nikola Valerjev Date: Sat, 10 Dec 2005 11:59:15 +0000 Subject: [PATCH] [ARM] 3200/1: Singlestep over ARM BX and BLX instructions using ptrace fix Patch from Nikola Valerjev Single stepping an application using ptrace() fails over ARM instructions BX and BLX. Steps to reproduce: Compile and link the following files main.c ----- void foo(); int main() { foo(); return 0; } foo.s ----- .text .globl foo foo: BX LR Using ptrace() functionality, run to main(), and start singlestepping. Singlestep over \"BX LR\" instruction won\'t transfer the control back to main, but run the code to completion. This problems seems to be in the function get_branch_address() in arch/arm/kernel/ptrace.c. The function doesn\'t seem to recognize BX and BLX instructions as branches. BX and BLX instructions can be used to convert from ARM to Thumb mode if the target address has the low bit set. However, they are also perfectly legal in the ARM only mode. Although other things in the kernel seem to indicate that only ARM mode is accepted (and not Thumb), many compilers will generate BX and BLX instructions even when generating ARM only code. Signed-off-by: Nikola Valerjev Signed-off-by: Russell King --- arch/arm/kernel/ptrace.c | 9 +++++++++ 1 file changed, 9 insertions(+) diff --git a/arch/arm/kernel/ptrace.c b/arch/arm/kernel/ptrace.c index 9a340e790da..2b84f78d7b0 100644 --- a/arch/arm/kernel/ptrace.c +++ b/arch/arm/kernel/ptrace.c @@ -242,6 +242,15 @@ get_branch_address(struct task_struct *child, unsigned long pc, unsigned long in */ long aluop1, aluop2, ccbit; + if ((insn & 0x0fffffd0) == 0x012fff10) { + /* + * bx or blx + */ + alt = get_user_reg(child, insn & 15); + break; + } + + if ((insn & 0xf000) != 0xf000) break; -- 2.20.1