perf probe: Show correct source lines of probes on kmodules

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)
  ----

Reported-by: Arnaldo Carvalho de Melo <acme@kernel.org>
Signed-off-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Wang Nan <wangnan0@huawei.com>
Link: http://lkml.kernel.org/r/20150930164132.3733.24643.stgit@localhost.localdomain
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

diff --git a/tools/perf/util/probe-event.c b/tools/perf/util/probe-event.c
index 5d68f68..65be284 100644 (file)
--- a/tools/perf/util/probe-event.c
+++ b/tools/perf/util/probe-event.c
@@ -137,7 +137,8 @@ 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;
@@ -146,12 +147,14 @@ 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;
 }
@@ -245,12 +248,14 @@ 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);
@@ -517,8 +522,10 @@ 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;
        }
@@ -1884,8 +1891,12 @@ 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 (file)
--- 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;