[PATCH perf/core 3/5] [BUGFIX] perf-probe: Show correct source lines of probes on kmodules

[Masami Hiramatsu]

Perf probe always failed to find appropriate line numbers
because of failing to find .text start address offset from
debuginfo.

e.g.
  ----
  # ./perf probe -m pcspkr pcspkr_event:5
  Added new events:
    probe:pcspkr_event   (on pcspkr_event:5 in pcspkr)
    probe:pcspkr_event_1 (on pcspkr_event:5 in pcspkr)

  You can now use it in all perf tools, such as:

          perf record -e probe:pcspkr_event_1 -aR sleep 1

  # ./perf probe -l
  Failed to find debug information for address ffffffffa031f006
  Failed to find debug information for address ffffffffa031f016
    probe:pcspkr_event   (on pcspkr_event+6 in pcspkr)
    probe:pcspkr_event_1 (on pcspkr_event+22 in pcspkr)
  ----

This fixes the above issue as below.
1. Get the relative address of the symbol in .text by using
   map->start.
2. Adjust the address by adding the offset of .text section
   in the kernel module binary.

With this fix, perf probe -l shows lines correctly.
  ----
  # ./perf probe -l
    probe:pcspkr_event   (on pcspkr_event:5@drivers/input/misc/pcspkr.c
  in pcspkr)
    probe:pcspkr_event_1 (on pcspkr_event:5@drivers/input/misc/pcspkr.c
  in pcspkr)
  ----

Signed-off-by: Masami Hiramatsu <masami.hiramatsu.pt@xxxxxxxxxxx>
Reported-by: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
---
 tools/perf/util/probe-event.c  |   35 ++++++++++++++++++++++-----------
 tools/perf/util/probe-finder.c |   42 ++++++++++++++++++++++++++++++++++++++++
 2 files changed, 65 insertions(+), 12 deletions(-)

diff --git a/tools/perf/util/probe-event.c b/tools/perf/util/probe-event.c
index 7eb0239..57a8cad 100644
--- a/tools/perf/util/probe-event.c
+++ b/tools/perf/util/probe-event.c
@@ -136,7 +136,8 @@ static struct ref_reloc_sym *kernel_get_ref_reloc_sym(void)
 	return kmap->ref_reloc_sym;
 }
 
-static u64 kernel_get_symbol_address_by_name(const char *name, bool reloc)
+static int kernel_get_symbol_address_by_name(const char *name, u64 *addr,
+					     bool reloc, bool reladdr)
 {
 	struct ref_reloc_sym *reloc_sym;
 	struct symbol *sym;
@@ -145,12 +146,14 @@ static u64 kernel_get_symbol_address_by_name(const char *name, bool reloc)
 	/* ref_reloc_sym is just a label. Need a special fix*/
 	reloc_sym = kernel_get_ref_reloc_sym();
 	if (reloc_sym && strcmp(name, reloc_sym->name) == 0)
-		return (reloc) ? reloc_sym->addr : reloc_sym->unrelocated_addr;
+		*addr = (reloc) ? reloc_sym->addr : reloc_sym->unrelocated_addr;
 	else {
 		sym = __find_kernel_function_by_name(name, &map);
-		if (sym)
-			return map->unmap_ip(map, sym->start) -
-				((reloc) ? 0 : map->reloc);
+		if (!sym)
+			return -ENOENT;
+		*addr = map->unmap_ip(map, sym->start) -
+			((reloc) ? 0 : map->reloc) -
+			((reladdr) ? map->start : 0);
 	}
 	return 0;
 }
@@ -244,12 +247,14 @@ static void clear_probe_trace_events(struct probe_trace_event *tevs, int ntevs)
 static bool kprobe_blacklist__listed(unsigned long address);
 static bool kprobe_warn_out_range(const char *symbol, unsigned long address)
 {
-	u64 etext_addr;
+	u64 etext_addr = 0;
+	int ret;
 
 	/* Get the address of _etext for checking non-probable text symbol */
-	etext_addr = kernel_get_symbol_address_by_name("_etext", false);
+	ret = kernel_get_symbol_address_by_name("_etext", &etext_addr,
+						false, false);
 
-	if (etext_addr != 0 && etext_addr < address)
+	if (ret == 0 && etext_addr < address)
 		pr_warning("%s is out of .text, skip it.\n", symbol);
 	else if (kprobe_blacklist__listed(address))
 		pr_warning("%s is blacklisted function, skip it.\n", symbol);
@@ -516,8 +521,10 @@ static int find_perf_probe_point_from_dwarf(struct probe_trace_point *tp,
 			goto error;
 		addr += stext;
 	} else if (tp->symbol) {
-		addr = kernel_get_symbol_address_by_name(tp->symbol, false);
-		if (addr == 0)
+		/* If the module is given, this returns relative address */
+		ret = kernel_get_symbol_address_by_name(tp->symbol, &addr,
+							false, !!tp->module);
+		if (ret != 0)
 			goto error;
 		addr += tp->offset;
 	}
@@ -1883,8 +1890,12 @@ static int find_perf_probe_point_from_map(struct probe_trace_point *tp,
 			goto out;
 		sym = map__find_symbol(map, addr, NULL);
 	} else {
-		if (tp->symbol)
-			addr = kernel_get_symbol_address_by_name(tp->symbol, true);
+		if (tp->symbol && !addr) {
+			ret = kernel_get_symbol_address_by_name(tp->symbol,
+							&addr, true, false);
+			if (ret < 0)
+				goto out;
+		}
 		if (addr) {
 			addr += tp->offset;
 			sym = __find_kernel_function(addr, &map);
diff --git a/tools/perf/util/probe-finder.c b/tools/perf/util/probe-finder.c
index 35f905f..f0708ff 100644
--- a/tools/perf/util/probe-finder.c
+++ b/tools/perf/util/probe-finder.c
@@ -1402,6 +1402,41 @@ int debuginfo__find_available_vars_at(struct debuginfo *dbg,
 	return (ret < 0) ? ret : af.nvls;
 }
 
+/* For the kernel module, we need a special code to get a DIE */
+static int debuginfo__get_text_offset(struct debuginfo *dbg, Dwarf_Addr *offs)
+{
+	int n, i;
+	Elf32_Word shndx;
+	Elf_Scn *scn;
+	Elf *elf;
+	GElf_Shdr mem, *shdr;
+	const char *p;
+
+	elf = dwfl_module_getelf(dbg->mod, &dbg->bias);
+	if (!elf)
+		return -EINVAL;
+
+	/* Get the number of relocations */
+	n = dwfl_module_relocations(dbg->mod);
+	if (n < 0)
+		return -ENOENT;
+	/* Search the relocation related .text section */
+	for (i = 0; i < n; i++) {
+		p = dwfl_module_relocation_info(dbg->mod, i, &shndx);
+		if (strcmp(p, ".text") == 0) {
+			/* OK, get the section header */
+			scn = elf_getscn(elf, shndx);
+			if (!scn)
+				return -ENOENT;
+			shdr = gelf_getshdr(scn, &mem);
+			if (!shdr)
+				return -ENOENT;
+			*offs = shdr->sh_addr;
+		}
+	}
+	return 0;
+}
+
 /* Reverse search */
 int debuginfo__find_probe_point(struct debuginfo *dbg, unsigned long addr,
 				struct perf_probe_point *ppt)
@@ -1410,9 +1445,16 @@ int debuginfo__find_probe_point(struct debuginfo *dbg, unsigned long addr,
 	Dwarf_Addr _addr = 0, baseaddr = 0;
 	const char *fname = NULL, *func = NULL, *basefunc = NULL, *tmp;
 	int baseline = 0, lineno = 0, ret = 0;
+	bool reloc = false;
 
+retry:
 	/* Find cu die */
 	if (!dwarf_addrdie(dbg->dbg, (Dwarf_Addr)addr, &cudie)) {
+		if (!reloc && debuginfo__get_text_offset(dbg, &baseaddr) == 0) {
+			addr += baseaddr;
+			reloc = true;
+			goto retry;
+		}
 		pr_warning("Failed to find debug information for address %lx\n",
 			   addr);
 		ret = -EINVAL;

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