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authorPeter Zijlstra <peterz@infradead.org>2019-05-07 23:25:54 +0200
committerIngo Molnar <mingo@kernel.org>2019-06-25 10:23:47 +0200
commit3c88c692c28746473791276f8b42d2c989d6cbe6 (patch)
tree51cb03ef4cbb611f42ea43c8737be894991b656b /arch/x86/kernel/ftrace_32.S
parentea1ed38dba64b64a245ab8ca1406269d17b99485 (diff)
x86/stackframe/32: Provide consistent pt_regs
Currently pt_regs on x86_32 has an oddity in that kernel regs (!user_mode(regs)) are short two entries (esp/ss). This means that any code trying to use them (typically: regs->sp) needs to jump through some unfortunate hoops. Change the entry code to fix this up and create a full pt_regs frame. This then simplifies various trampolines in ftrace and kprobes, the stack unwinder, ptrace, kdump and kgdb. Much thanks to Josh for help with the cleanups! Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Reviewed-by: Josh Poimboeuf <jpoimboe@redhat.com> Acked-by: Masami Hiramatsu <mhiramat@kernel.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'arch/x86/kernel/ftrace_32.S')
-rw-r--r--arch/x86/kernel/ftrace_32.S75
1 files changed, 42 insertions, 33 deletions
diff --git a/arch/x86/kernel/ftrace_32.S b/arch/x86/kernel/ftrace_32.S
index 0344c3aad4a5..073aab525d80 100644
--- a/arch/x86/kernel/ftrace_32.S
+++ b/arch/x86/kernel/ftrace_32.S
@@ -10,6 +10,7 @@
#include <asm/ftrace.h>
#include <asm/nospec-branch.h>
#include <asm/frame.h>
+#include <asm/asm-offsets.h>
# define function_hook __fentry__
EXPORT_SYMBOL(__fentry__)
@@ -90,26 +91,38 @@ END(ftrace_caller)
ENTRY(ftrace_regs_caller)
/*
- * i386 does not save SS and ESP when coming from kernel.
- * Instead, to get sp, &regs->sp is used (see ptrace.h).
- * Unfortunately, that means eflags must be at the same location
- * as the current return ip is. We move the return ip into the
- * regs->ip location, and move flags into the return ip location.
+ * We're here from an mcount/fentry CALL, and the stack frame looks like:
+ *
+ * <previous context>
+ * RET-IP
+ *
+ * The purpose of this function is to call out in an emulated INT3
+ * environment with a stack frame like:
+ *
+ * <previous context>
+ * gap / RET-IP
+ * gap
+ * gap
+ * gap
+ * pt_regs
+ *
+ * We do _NOT_ restore: ss, flags, cs, gs, fs, es, ds
*/
- pushl $__KERNEL_CS
- pushl 4(%esp) /* Save the return ip */
- pushl $0 /* Load 0 into orig_ax */
+ subl $3*4, %esp # RET-IP + 3 gaps
+ pushl %ss # ss
+ pushl %esp # points at ss
+ addl $5*4, (%esp) # make it point at <previous context>
+ pushfl # flags
+ pushl $__KERNEL_CS # cs
+ pushl 7*4(%esp) # ip <- RET-IP
+ pushl $0 # orig_eax
+
pushl %gs
pushl %fs
pushl %es
pushl %ds
- pushl %eax
-
- /* Get flags and place them into the return ip slot */
- pushf
- popl %eax
- movl %eax, 8*4(%esp)
+ pushl %eax
pushl %ebp
pushl %edi
pushl %esi
@@ -119,24 +132,25 @@ ENTRY(ftrace_regs_caller)
ENCODE_FRAME_POINTER
- movl 12*4(%esp), %eax /* Load ip (1st parameter) */
- subl $MCOUNT_INSN_SIZE, %eax /* Adjust ip */
- movl 15*4(%esp), %edx /* Load parent ip (2nd parameter) */
- movl function_trace_op, %ecx /* Save ftrace_pos in 3rd parameter */
- pushl %esp /* Save pt_regs as 4th parameter */
+ movl PT_EIP(%esp), %eax # 1st argument: IP
+ subl $MCOUNT_INSN_SIZE, %eax
+ movl 21*4(%esp), %edx # 2nd argument: parent ip
+ movl function_trace_op, %ecx # 3rd argument: ftrace_pos
+ pushl %esp # 4th argument: pt_regs
GLOBAL(ftrace_regs_call)
call ftrace_stub
- addl $4, %esp /* Skip pt_regs */
+ addl $4, %esp # skip 4th argument
- /* restore flags */
- push 14*4(%esp)
- popf
+ /* place IP below the new SP */
+ movl PT_OLDESP(%esp), %eax
+ movl PT_EIP(%esp), %ecx
+ movl %ecx, -4(%eax)
- /* Move return ip back to its original location */
- movl 12*4(%esp), %eax
- movl %eax, 14*4(%esp)
+ /* place EAX below that */
+ movl PT_EAX(%esp), %ecx
+ movl %ecx, -8(%eax)
popl %ebx
popl %ecx
@@ -144,14 +158,9 @@ GLOBAL(ftrace_regs_call)
popl %esi
popl %edi
popl %ebp
- popl %eax
- popl %ds
- popl %es
- popl %fs
- popl %gs
- /* use lea to not affect flags */
- lea 3*4(%esp), %esp /* Skip orig_ax, ip and cs */
+ lea -8(%eax), %esp
+ popl %eax
jmp .Lftrace_ret