Messages in this thread | | | Subject | Re: [PATCH v2 2/2] perf uprobe: Skip prologue if program compiled without optimization | From | Ravi Bangoria <> | Date | Sat, 13 Aug 2016 19:15:53 +0530 |
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Hi Masami, Arnaldo,
Any updates on this?
Thanks, Ravi
On Wednesday 03 August 2016 02:28 PM, Ravi Bangoria wrote: > Function prologue prepares stack and registers before executing function > logic. When target program is compiled without optimization, function > parameter information is only valid after prologue. When we probe entrypc > of the function, and try to record function parameter, it contains > garbage value. > > For example, > $ vim test.c > #include <stdio.h> > > void foo(int i) > { > printf("i: %d\n", i); > } > > int main() > { > foo(42); > return 0; > } > > $ gcc -g test.c -o test > $ objdump -dl test | less > foo(): > /home/ravi/test.c:4 > 400536: 55 push %rbp > 400537: 48 89 e5 mov %rsp,%rbp > 40053a: 48 83 ec 10 sub -bashx10,%rsp > 40053e: 89 7d fc mov %edi,-0x4(%rbp) > /home/ravi/test.c:5 > 400541: 8b 45 fc mov -0x4(%rbp),%eax > ... > ... > main(): > /home/ravi/test.c:9 > 400558: 55 push %rbp > 400559: 48 89 e5 mov %rsp,%rbp > /home/ravi/test.c:10 > 40055c: bf 2a 00 00 00 mov -bashx2a,%edi > 400561: e8 d0 ff ff ff callq 400536 <foo> > /home/ravi/test.c:11 > > $ ./perf probe -x ./test 'foo i' > $ cat /sys/kernel/debug/tracing/uprobe_events > p:probe_test/foo /home/ravi/test:0x0000000000000536 i=-12(%sp):s32 > > $ ./perf record -e probe_test:foo ./test > $ ./perf script > test 5778 [001] 4918.562027: probe_test:foo: (400536) i=0 > > Here variable 'i' is passed via stack which is pushed on stack at > 0x40053e. But we are probing at 0x400536. > > To resolve this issues, we need to probe on next instruction after > prologue. gdb and systemtap also does same thing. I've implemented > this patch based on approach systemtap has used. > > After applying patch: > > $ ./perf probe -x ./test 'foo i' > $ cat /sys/kernel/debug/tracing/uprobe_events > p:probe_test/foo /home/ravi/test:0x0000000000000541 i=-4(%bp):s32 > > $ ./perf record -e probe_test:foo ./test > $ ./perf script > test 6300 [001] 5877.879327: probe_test:foo: (400541) i=42 > > No need to skip prologue for optimized case since debug info is correct > for each instructions for -O2 -g. For more details please visit: > https://bugzilla.redhat.com/show_bug.cgi?id=612253#c6 > > Signed-off-by: Ravi Bangoria <ravi.bangoria@linux.vnet.ibm.com> > --- > Changes in v2: > - Skipping prologue only when any ARG is either C variable, $params > or $vars. > - Probe on line(:1) may not be always possible. Recommend only address > to force probe on function entry. > > tools/perf/util/probe-finder.c | 164 +++++++++++++++++++++++++++++++++++++++++ > 1 file changed, 164 insertions(+) > > diff --git a/tools/perf/util/probe-finder.c b/tools/perf/util/probe-finder.c > index f2d9ff0..b2bc77c 100644 > --- a/tools/perf/util/probe-finder.c > +++ b/tools/perf/util/probe-finder.c > @@ -892,6 +892,169 @@ static int find_probe_point_lazy(Dwarf_Die *sp_die, struct probe_finder *pf) > return die_walk_lines(sp_die, probe_point_lazy_walker, pf); > } > > +static bool var_has_loclist(Dwarf_Die *die) > +{ > + Dwarf_Attribute loc; > + int tag = dwarf_tag(die); > + > + if (tag != DW_TAG_formal_parameter && > + tag != DW_TAG_variable) > + return false; > + > + return (dwarf_attr_integrate(die, DW_AT_location, &loc) && > + dwarf_whatform(&loc) == DW_FORM_sec_offset); > +} > + > +/* > + * For any object in given CU whose DW_AT_location is a location list, > + * target program is compiled with optimization. > + */ > +static bool optimized_target(Dwarf_Die *die) > +{ > + Dwarf_Die tmp_die; > + > + if (var_has_loclist(die)) > + return true; > + > + if (!dwarf_child(die, &tmp_die) && optimized_target(&tmp_die)) > + return true; > + > + if (!dwarf_siblingof(die, &tmp_die) && optimized_target(&tmp_die)) > + return true; > + > + return false; > +} > + > +static bool get_entrypc_idx(Dwarf_Lines *lines, unsigned long nr_lines, > + Dwarf_Addr pf_addr, unsigned long *entrypc_idx) > +{ > + unsigned long i; > + Dwarf_Addr addr; > + > + for (i = 0; i < nr_lines; i++) { > + if (dwarf_lineaddr(dwarf_onesrcline(lines, i), &addr)) > + return false; > + > + if (addr == pf_addr) { > + *entrypc_idx = i; > + return true; > + } > + } > + return false; > +} > + > +static bool get_postprologue_addr(unsigned long entrypc_idx, > + Dwarf_Lines *lines, > + unsigned long nr_lines, > + Dwarf_Addr highpc, > + Dwarf_Addr *postprologue_addr) > +{ > + unsigned long i; > + int entrypc_lno, lno; > + Dwarf_Line *line; > + Dwarf_Addr addr; > + bool p_end; > + > + /* entrypc_lno is actual source line number */ > + line = dwarf_onesrcline(lines, entrypc_idx); > + if (dwarf_lineno(line, &entrypc_lno)) > + return false; > + > + for (i = entrypc_idx; i < nr_lines; i++) { > + line = dwarf_onesrcline(lines, i); > + > + if (dwarf_lineaddr(line, &addr) || > + dwarf_lineno(line, &lno) || > + dwarf_lineprologueend(line, &p_end)) > + return false; > + > + /* highpc is exclusive. [entrypc,highpc) */ > + if (addr >= highpc) > + break; > + > + /* clang supports prologue-end marker */ > + if (p_end) > + break; > + > + /* Actual next line in source */ > + if (lno != entrypc_lno) > + break; > + > + /* > + * Single source line can have multiple line records. > + * For Example, > + * void foo() { printf("hello\n"); } > + * contains two line records. One points to declaration and > + * other points to printf() line. Variable 'lno' won't get > + * incremented in this case but 'i' will. > + */ > + if (i != entrypc_idx) > + break; > + } > + > + dwarf_lineaddr(line, postprologue_addr); > + if (*postprologue_addr >= highpc) > + dwarf_lineaddr(dwarf_onesrcline(lines, i - 1), > + postprologue_addr); > + > + return true; > +} > + > +static void __skip_prologue(Dwarf_Die *sp_die, struct probe_finder *pf) > +{ > + unsigned long nr_lines = 0, entrypc_idx = 0; > + Dwarf_Lines *lines = NULL; > + Dwarf_Addr postprologue_addr; > + Dwarf_Addr highpc; > + > + if (dwarf_highpc(sp_die, &highpc)) > + return; > + > + if (dwarf_getsrclines(&pf->cu_die, &lines, &nr_lines)) > + return; > + > + if (!get_entrypc_idx(lines, nr_lines, pf->addr, &entrypc_idx)) > + return; > + > + if (!get_postprologue_addr(entrypc_idx, lines, nr_lines, > + highpc, &postprologue_addr)) > + return; > + > + pf->addr = postprologue_addr; > +} > + > +static void skip_prologue(Dwarf_Die *sp_die, struct probe_finder *pf) > +{ > + struct perf_probe_point *pp = &pf->pev->point; > + > + /* Not uprobe? */ > + if (!pf->pev->uprobes) > + return; > + > + /* Compiled with optimization? */ > + if (optimized_target(&pf->cu_die)) > + return; > + > + /* Don't know entrypc? */ > + if (!pf->addr) > + return; > + > + /* Only FUNC and FUNC@SRC are eligible. */ > + if (!pp->function || pp->line || pp->retprobe || pp->lazy_line || > + pp->offset || pp->abs_address) > + return; > + > + /* Not interested in func parameter? */ > + if (!perf_probe_with_var(pf->pev)) > + return; > + > + pr_info("Target program is compiled without optimization. Skipping prologue.\n" > + "Probe on address 0x%lx to force probing at the function entry.\n\n", > + pf->addr); > + > + __skip_prologue(sp_die, pf); > +} > + > static int probe_point_inline_cb(Dwarf_Die *in_die, void *data) > { > struct probe_finder *pf = data; > @@ -954,6 +1117,7 @@ static int probe_point_search_cb(Dwarf_Die *sp_die, void *data) > if (pp->lazy_line) > param->retval = find_probe_point_lazy(sp_die, pf); > else { > + skip_prologue(sp_die, pf); > pf->addr += pp->offset; > /* TODO: Check the address in this function */ > param->retval = call_probe_finder(sp_die, pf);
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