Commit 4d99e509 authored by Leon Hwang's avatar Leon Hwang Committed by Andrii Nakryiko
Browse files

bpf, bpftool: Fix incorrect disasm pc 

This patch addresses the bpftool issue "Wrong callq address displayed"[0].

The issue stemmed from an incorrect program counter (PC) value used during
disassembly with LLVM or libbfd.

For LLVM: The PC argument must represent the actual address in the kernel
to compute the correct relative address.

For libbfd: The relative address can be adjusted by adding func_ksym within
the custom info->print_address_func to yield the correct address.

Links:
[0] https://github.com/libbpf/bpftool/issues/109



Changes:
v2 -> v3:
  * Address comment from Quentin:
    * Remove the typedef.

v1 -> v2:
  * Fix the broken libbfd disassembler.

Fixes: e1947c75 ("bpftool: Refactor disassembler for JIT-ed programs")
Signed-off-by: default avatarLeon Hwang <leon.hwang@linux.dev>
Signed-off-by: default avatarAndrii Nakryiko <andrii@kernel.org>
Tested-by: default avatarQuentin Monnet <qmo@kernel.org>
Reviewed-by: default avatarQuentin Monnet <qmo@kernel.org>
Acked-by: default avatarYonghong Song <yonghong.song@linux.dev>
Link: https://lore.kernel.org/bpf/20241031152844.68817-1-leon.hwang@linux.dev
parent e5e4799e

tools/bpf/bpftool/jit_disasm.c

+29 −11
Original line number Diff line number Diff line
@@ -80,7 +80,8 @@ symbol_lookup_callback(__maybe_unused void *disasm_info, 
static int

init_context(disasm_ctx_t *ctx, const char *arch,

	     __maybe_unused const char *disassembler_options,

	     __maybe_unused unsigned char *image, __maybe_unused ssize_t len)

	     __maybe_unused unsigned char *image, __maybe_unused ssize_t len,

	     __maybe_unused __u64 func_ksym)

{

	char *triple;
@@ -109,12 +110,13 @@ static void destroy_context(disasm_ctx_t *ctx) 
}



static int

disassemble_insn(disasm_ctx_t *ctx, unsigned char *image, ssize_t len, int pc)

disassemble_insn(disasm_ctx_t *ctx, unsigned char *image, ssize_t len, int pc,

		 __u64 func_ksym)

{

	char buf[256];

	int count;



	count = LLVMDisasmInstruction(*ctx, image + pc, len - pc, pc,

	count = LLVMDisasmInstruction(*ctx, image + pc, len - pc, func_ksym + pc,

				      buf, sizeof(buf));

	if (json_output)

		printf_json(buf);
@@ -136,8 +138,21 @@ int disasm_init(void) 
#ifdef HAVE_LIBBFD_SUPPORT

#define DISASM_SPACER "\t"



struct disasm_info {

	struct disassemble_info info;

	__u64 func_ksym;

};



static void disasm_print_addr(bfd_vma addr, struct disassemble_info *info)

{

	struct disasm_info *dinfo = container_of(info, struct disasm_info, info);



	addr += dinfo->func_ksym;

	generic_print_address(addr, info);

}



typedef struct {

	struct disassemble_info *info;

	struct disasm_info *info;

	disassembler_ftype disassemble;

	bfd *bfdf;

} disasm_ctx_t;
@@ -215,7 +230,7 @@ static int fprintf_json_styled(void *out, 


static int init_context(disasm_ctx_t *ctx, const char *arch,

			const char *disassembler_options,

			unsigned char *image, ssize_t len)

			unsigned char *image, ssize_t len, __u64 func_ksym)

{

	struct disassemble_info *info;

	char tpath[PATH_MAX];
@@ -238,12 +253,13 @@ static int init_context(disasm_ctx_t *ctx, const char *arch, 
	}

	bfdf = ctx->bfdf;



	ctx->info = malloc(sizeof(struct disassemble_info));

	ctx->info = malloc(sizeof(struct disasm_info));

	if (!ctx->info) {

		p_err("mem alloc failed");

		goto err_close;

	}

	info = ctx->info;

	ctx->info->func_ksym = func_ksym;

	info = &ctx->info->info;



	if (json_output)

		init_disassemble_info_compat(info, stdout,
@@ -272,6 +288,7 @@ static int init_context(disasm_ctx_t *ctx, const char *arch, 
		info->disassembler_options = disassembler_options;

	info->buffer = image;

	info->buffer_length = len;

	info->print_address_func = disasm_print_addr;



	disassemble_init_for_target(info);
@@ -304,9 +321,10 @@ static void destroy_context(disasm_ctx_t *ctx) 


static int

disassemble_insn(disasm_ctx_t *ctx, __maybe_unused unsigned char *image,

		 __maybe_unused ssize_t len, int pc)

		 __maybe_unused ssize_t len, int pc,

		 __maybe_unused __u64 func_ksym)

{

	return ctx->disassemble(pc, ctx->info);

	return ctx->disassemble(pc, &ctx->info->info);

}



int disasm_init(void)
@@ -331,7 +349,7 @@ int disasm_print_insn(unsigned char *image, ssize_t len, int opcodes, 
	if (!len)

		return -1;



	if (init_context(&ctx, arch, disassembler_options, image, len))

	if (init_context(&ctx, arch, disassembler_options, image, len, func_ksym))

		return -1;



	if (json_output)
@@ -360,7 +378,7 @@ int disasm_print_insn(unsigned char *image, ssize_t len, int opcodes, 
			printf("%4x:" DISASM_SPACER, pc);

		}



		count = disassemble_insn(&ctx, image, len, pc);

		count = disassemble_insn(&ctx, image, len, pc, func_ksym);



		if (json_output) {

			/* Operand array, was started in fprintf_json. Before