On 18/05/26 3:10 am, [email protected] wrote:
From: Abhishek Dubey <[email protected]>
Move the long branch address space to the bottom of the long
branch stub. This allows uninterrupted disassembly until the
last 8 bytes. Exclude these last bytes from the overall
program length to prevent failure in assembly generation.
Also, align dummy_tramp_addr field with 8-byte boundary.
Following is disassembler output for test program with moved down
dummy_tramp_addr field:
.....
.....
pc:68 left:44 a6 03 08 7c : mtlr 0
pc:72 left:40 bc ff ff 4b : b .-68
pc:76 left:36 a6 02 68 7d : mflr 11
pc:80 left:32 05 00 9f 42 : bcl 20, 31, .+4
pc:84 left:28 a6 02 88 7d : mflr 12
pc:88 left:24 14 00 8c e9 : ld 12, 20(12)
pc:92 left:20 a6 03 89 7d : mtctr 12
pc:96 left:16 a6 03 68 7d : mtlr 11
pc:100 left:12 20 04 80 4e : bctr
pc:104 left:8 c0 34 1d 00 :
Failure log:
Can't disasm instruction at offset 104: c0 34 1d 00 00 00 00 c0
Disassembly logic can truncate at 104, ignoring last 8 bytes.
Update the dummy_tramp_addr field offset calculation from the end
of the program to reflect its new location, for bpf_arch_text_poke()
to update the actual trampoline's address in this field.
All BPF trampoline selftests continue to pass with this patch applied.
Signed-off-by: Abhishek Dubey <[email protected]>
---
arch/powerpc/net/bpf_jit_comp.c | 34 +++++++++++++++++++--------------
1 file changed, 20 insertions(+), 14 deletions(-)
diff --git a/arch/powerpc/net/bpf_jit_comp.c b/arch/powerpc/net/bpf_jit_comp.c
index ef7614177cb1..b73bc9295c31 100644
--- a/arch/powerpc/net/bpf_jit_comp.c
+++ b/arch/powerpc/net/bpf_jit_comp.c
@@ -57,19 +57,21 @@ void bpf_jit_build_fentry_stubs(u32 *image, u32 *fimage,
struct codegen_context
* In the final pass, align the mis-aligned dummy_tramp_addr field
* in the fimage. The alignment NOP must appear before OOL stub,
* to make ool_stub_idx & long_branch_stub_idx constant from end.
+ *
+ * The dummy_tramp_addr field is placed at bottom of Long branch stub.
*/
#ifdef CONFIG_PPC64
if (fimage && image) {
/*
* pc points to first instruction of OOL stub,
- * dummy_tramp_addr is past 4/3 instructions depending on
+ * dummy_tramp_addr is past 11/10 instructions depending on
* CONFIG_PPC_FTRACE_OUT_OF_LINE is enabled/not respectively.
*
* The decision to emit alignment NOP must depend on the
alignment
* of dummy_tramp_addr field.
*/
unsigned long pc = (unsigned long)fimage + CTX_NIA(ctx);
- pc += IS_ENABLED(CONFIG_PPC_FTRACE_OUT_OF_LINE) ? 4 : 3;
+ pc += IS_ENABLED(CONFIG_PPC_FTRACE_OUT_OF_LINE) ? 11 : 10;
To get the address, should multiply the instruction count with 4..
pc += (IS_ENABLED(CONFIG_PPC_FTRACE_OUT_OF_LINE) ? 11 : 10) * 4;
Also, pc may not be appropriate name here. We are essentially
calculating the pointer address of dummy_tramp_addr. `addrp` maybe?
- Hari
