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    SubjectRe: [PATCH V2 9/9] perf buildid-cache: Check relocation when checking for existing kcore
    On 29/01/14 21:14, Arnaldo Carvalho de Melo wrote:
    > Em Wed, Jan 29, 2014 at 04:14:44PM +0200, Adrian Hunter escreveu:
    >> perf buildid-cache does not make another
    >> copy of kcore if the buildid and modules
    >> match an existing copy. That does not
    >
    > Humm, what is the problem? Having the ref reloc symbol we can fix things
    > up, no? I.e. just using map->reloc the old kcore copy should be ok to
    > use, no need to replace the kcore copy in the cache. Or am I missing
    > something?

    The current implementation works on the basis that kcore
    matches the perf data recorded. This is just a fix for that.

    I am afraid it is that way because it meets my needs.
    I did not think of allowing for relocation because I
    need to be able to walk the code. Relocation was one
    of the things I was trying to avoid.

    For me making a copy of kcore is far superior because
    it can be made to have the jump labels mostly the
    right way around too. e.g. run a dummy perf record
    while making the copy.

    >
    > - Arnaldo
    >
    >> take into account the possibility that
    >> the kernel has been relocated. Extend
    >> the check to check if the reference
    >> relocation symbol matches too, otherwise
    >> do make a copy.
    >>
    >> Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
    >> ---
    >> tools/perf/builtin-buildid-cache.c | 33 +++++++++++++++++++++++++++++----
    >> 1 file changed, 29 insertions(+), 4 deletions(-)
    >>
    >> diff --git a/tools/perf/builtin-buildid-cache.c b/tools/perf/builtin-buildid-cache.c
    >> index cfede86..b22dbb1 100644
    >> --- a/tools/perf/builtin-buildid-cache.c
    >> +++ b/tools/perf/builtin-buildid-cache.c
    >> @@ -63,11 +63,35 @@ static int build_id_cache__kcore_dir(char *dir, size_t sz)
    >> return 0;
    >> }
    >>
    >> +static bool same_kallsyms_reloc(const char *from_dir, char *to_dir)
    >> +{
    >> + char from[PATH_MAX];
    >> + char to[PATH_MAX];
    >> + const char *name;
    >> + u64 addr1 = 0, addr2 = 0;
    >> + int i;
    >> +
    >> + scnprintf(from, sizeof(from), "%s/kallsyms", from_dir);
    >> + scnprintf(to, sizeof(to), "%s/kallsyms", to_dir);
    >> +
    >> + for (i = 0; (name = ref_reloc_sym_names[i]) != NULL; i++) {
    >> + addr1 = kallsyms__get_function_start(from, name);
    >> + if (addr1)
    >> + break;
    >> + }
    >> +
    >> + if (name)
    >> + addr2 = kallsyms__get_function_start(to, name);
    >> +
    >> + return addr1 == addr2;
    >> +}
    >> +
    >> static int build_id_cache__kcore_existing(const char *from_dir, char *to_dir,
    >> size_t to_dir_sz)
    >> {
    >> char from[PATH_MAX];
    >> char to[PATH_MAX];
    >> + char to_subdir[PATH_MAX];
    >> struct dirent *dent;
    >> int ret = -1;
    >> DIR *d;
    >> @@ -86,10 +110,11 @@ static int build_id_cache__kcore_existing(const char *from_dir, char *to_dir,
    >> continue;
    >> scnprintf(to, sizeof(to), "%s/%s/modules", to_dir,
    >> dent->d_name);
    >> - if (!compare_proc_modules(from, to)) {
    >> - scnprintf(to, sizeof(to), "%s/%s", to_dir,
    >> - dent->d_name);
    >> - strlcpy(to_dir, to, to_dir_sz);
    >> + scnprintf(to_subdir, sizeof(to_subdir), "%s/%s",
    >> + to_dir, dent->d_name);
    >> + if (!compare_proc_modules(from, to) &&
    >> + same_kallsyms_reloc(from_dir, to_subdir)) {
    >> + strlcpy(to_dir, to_subdir, to_dir_sz);
    >> ret = 0;
    >> break;
    >> }
    >> --
    >> 1.7.11.7
    >
    >



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