[ktap] Re: [PATCH] add new symbol module to search symbols in DSO (for uprobes)
- From: Azat Khuzhin <a3at.mail@xxxxxxxxx>
- To: Yicheng <qycqycqycqycqyc@xxxxxxxxx>
- Date: Tue, 5 Nov 2013 08:22:47 +0400
On 5 Nov 2013 02:02, "Yicheng" <qycqycqycqycqyc@xxxxxxxxx> wrote:
>
> Looks good!
> The main concern in my view is the performance issue for ktap vm
interrupter.
> vm runs parse_events_resolve_symbol() to parse the symbol, but it may
> be the unnecessary burden for vm because it can be calculated in parser
> and written into bytecode. And I wonder whether or not the parse process
> consumes a lot of time.
I wasn't thinking about it.
>
> One suggestion about parse_events_resolve_symbol(): IMHO, strndup may
> be executed after checking whether r is a number, or it may do useless
> malloc operations when r is a number.
Nice catch, I resent updated patch.
Thanks.
>
>
> 2013/11/4 Azat Khuzhin <a3at.mail@xxxxxxxxx>
>>
>> This will allow to don't hardcoding addresses of functions in ktap
>> scripts, that use uprobes, but instead, use normal function names.
>>
>> Before this patch:
>> $ ktap -e 'trace probe:/path/to/bin:0xDEADBEAF' # instead some real
address
>>
>> After this path:
>> $ ktap -e 'trace probe:/path/to/bin:foo'
>>
>> Works also for ret probes (%return)
>> Requires libelf.
>>
>> Signed-off-by: Azat Khuzhin <a3at.mail@xxxxxxxxx>
>> ---
>> Makefile | 5 ++-
>> include/ktap_types.h | 2 +
>> userspace/eventdef.c | 34 +++++++++++++++
>> userspace/symbol.c | 114
+++++++++++++++++++++++++++++++++++++++++++++++++++
>> userspace/symbol.h | 32 +++++++++++++++
>> 5 files changed, 186 insertions(+), 1 deletion(-)
>> create mode 100644 userspace/symbol.c
>> create mode 100644 userspace/symbol.h
>>
>> diff --git a/Makefile b/Makefile
>> index 372b41a..344c82a 100644
>> --- a/Makefile
>> +++ b/Makefile
>> @@ -59,6 +59,8 @@ $(UDIR)/tstring.o: $(INTP)/tstring.c $(INC)/*
>> $(QUIET_CC)$(CC) $(DEBUGINFO_FLAG) $(KTAPC_CFLAGS) -o $@ -c $<
>> $(UDIR)/object.o: $(INTP)/object.c $(INC)/*
>> $(QUIET_CC)$(CC) $(DEBUGINFO_FLAG) $(KTAPC_CFLAGS) -o $@ -c $<
>> +$(UDIR)/symbol.o: $(UDIR)/symbol.c $(INC)/*
>> + $(QUIET_CC)$(CC) $(DEBUGINFO_FLAG) $(KTAPC_CFLAGS) -o $@ -c $<
>>
>> KTAPOBJS =
>> KTAPOBJS += $(UDIR)/lex.o
>> @@ -73,9 +75,10 @@ KTAPOBJS += $(UDIR)/opcode.o
>> KTAPOBJS += $(UDIR)/table.o
>> KTAPOBJS += $(UDIR)/tstring.o
>> KTAPOBJS += $(UDIR)/object.o
>> +KTAPOBJS += $(UDIR)/symbol.o
>>
>> ktap: $(KTAPOBJS)
>> - $(QUIET_LINK)$(CC) $(KTAPC_CFLAGS) -o $@ $(KTAPOBJS) -lpthread
>> + $(QUIET_LINK)$(CC) $(KTAPC_CFLAGS) -o $@ $(KTAPOBJS) -lpthread
-lelf
>>
>> KMISC := /lib/modules/$(KVERSION)/ktapvm/
>>
>> diff --git a/include/ktap_types.h b/include/ktap_types.h
>> index 1dae9d8..4e19f0b 100644
>> --- a/include/ktap_types.h
>> +++ b/include/ktap_types.h
>> @@ -600,5 +600,7 @@ extern ktap_global_state dummy_global_state;
>> #define KTAP_QL(x) "'" x "'"
>> #define KTAP_QS KTAP_QL("%s")
>>
>> +#define STRINGIFY(type) #type
>> +
>> #endif /* __KTAP_TYPES_H__ */
>>
>> diff --git a/userspace/eventdef.c b/userspace/eventdef.c
>> index 76a68ac..dab964a 100644
>> --- a/userspace/eventdef.c
>> +++ b/userspace/eventdef.c
>> @@ -29,6 +29,7 @@
>> #include "../include/ktap_types.h"
>> #include "../include/ktap_opcodes.h"
>> #include "ktapc.h"
>> +#include "symbol.h"
>>
>> static char tracing_events_path[] = "/sys/kernel/debug/tracing/events";
>>
>> @@ -305,6 +306,35 @@ static int parse_events_add_kprobe(char *old_event)
>>
>> #define UPROBE_EVENTS_PATH "/sys/kernel/debug/tracing/uprobe_events"
>>
>> +static char* parse_events_resolve_symbol(char *event, char *r)
>> +{
>> + char *colon;
>> + colon = strchr(event, ':');
>> +
>> + char *binary = strndup(event, colon - event);
>> + char *symbol = strndup(colon + 1 /* skip ":" */,
>> + r ? (r - 1 /* skip "%" */ - colon) : strlen((const char
*)colon));
>> +
>> + /**
>> + * Test whethere we have symbol address, or symbol name.
>> + * If second, than we need to scan dso to resolve it.
>> + */
>> + vaddr_t symbol_address;
>> + if ((sscanf(symbol, "%lx", &symbol_address) != 1) &&
>> + (symbol_address = find_symbol(binary, symbol))) {
>> + verbose_printf("symbol %s resolved to 0x%lx\n",
>> + event, symbol_address);
>> +
>> + event = realloc(event, strlen(event) +
(strlen(STRINGIFY(ULONG_MAX))));
>> + sprintf(event, "%s:0x%lx", binary, symbol_address);
>> + }
>> +
>> + free(binary);
>> + free(symbol);
>> +
>> + return event;
>> +}
>> +
>> static int parse_events_add_uprobe(char *old_event)
>> {
>> static int event_seq = 0;
>> @@ -326,6 +356,10 @@ static int parse_events_add_uprobe(char *old_event)
>> r = strstr(event, "%return");
>> if (r) {
>> memset(r, ' ', 7);
>> + }
>> + event = parse_events_resolve_symbol(event, r);
>> +
>> + if (r) {
>> snprintf(probe_event, 128, "r:uprobes/kp%d %s",
>> event_seq, event);
>> } else
>> diff --git a/userspace/symbol.c b/userspace/symbol.c
>> new file mode 100644
>> index 0000000..23333b8
>> --- /dev/null
>> +++ b/userspace/symbol.c
>> @@ -0,0 +1,114 @@
>> +/*
>> + * symbol.c
>> + *
>> + * This file is part of ktap by Jovi Zhangwei.
>> + *
>> + * Copyright (C) 2013 Azat Khuzhin <a3at.mail@xxxxxxxxx>.
>> + *
>> + * ktap is free software; you can redistribute it and/or modify it
>> + * under the terms and conditions of the GNU General Public License,
>> + * version 2, as published by the Free Software Foundation.
>> + *
>> + * ktap is distributed in the hope it will be useful, but WITHOUT
>> + * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
>> + * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public
License for
>> + * more details.
>> + *
>> + * You should have received a copy of the GNU General Public License
along with
>> + * this program; if not, write to the Free Software Foundation, Inc.,
>> + * 51 Franklin St - Fifth Floor, Boston, MA 02110-1301 USA.
>> + */
>> +
>> +#include "symbol.h"
>> +
>> +#include <stdio.h>
>> +#include <stdlib.h>
>> +
>> +#include <sys/types.h>
>> +#include <sys/stat.h>
>> +#include <unistd.h>
>> +#include <fcntl.h>
>> +#include <string.h>
>> +
>> +#include <libelf.h>
>> +
>> +
>> +/**
>> + * @return v_addr of "LOAD" program header, that have zero offset.
>> + */
>> +static vaddr_t find_load_address(Elf *elf)
>> +{
>> + GElf_Phdr header;
>> + size_t headers;
>> + vaddr_t address = 0;
>> +
>> + elf_getphdrnum(elf, &headers);
>> + while (headers-- > 0) {
>> + gelf_getphdr(elf, headers, &header);
>> + if (header.p_type != PT_LOAD || header.p_offset != 0)
>> + continue;
>> +
>> + address = header.p_vaddr;
>> + break;
>> + }
>> +
>> + return address;
>> +}
>> +
>> +static vaddr_t search_symbol(Elf *elf, const char *symbol)
>> +{
>> + Elf_Data *elf_data = NULL;
>> + Elf_Scn *scn = NULL;
>> + GElf_Sym sym;
>> + GElf_Shdr shdr;
>> +
>> + vaddr_t load_address = find_load_address(elf);
>> +
>> + if (!load_address)
>> + return 0;
>> +
>> + while ((scn = elf_nextscn(elf, scn))) {
>> + int i, symbols;
>> + char *current_symbol;
>> +
>> + gelf_getshdr(scn, &shdr);
>> +
>> + if (shdr.sh_type != SHT_SYMTAB)
>> + continue;
>> +
>> + elf_data = elf_getdata(scn, elf_data);
>> + symbols = shdr.sh_size / shdr.sh_entsize;
>> +
>> + for (i = 0; i < symbols; i++) {
>> + gelf_getsym(elf_data, i, &sym);
>> +
>> + if (GELF_ST_TYPE(sym.st_info) != STT_FUNC)
>> + continue;
>> +
>> + current_symbol = elf_strptr(elf, shdr.sh_link,
sym.st_name);
>> + if (!strcmp(current_symbol, symbol)) {
>> + return (sym.st_value - load_address);
>> + }
>> + }
>> + }
>> +
>> + return 0;
>> +}
>> +
>> +vaddr_t find_symbol(const char *exec, const char *symbol)
>> +{
>> + Elf *elf = NULL;
>> + int fd = 0;
>> + vaddr_t vaddr = 0;
>> +
>> + if (((fd = open(exec, O_RDONLY)) != -1) &&
>> + (elf_version(EV_CURRENT) != EV_NONE) &&
>> + (elf = elf_begin(fd, ELF_C_READ, NULL)))
>> + vaddr = search_symbol(elf, symbol);
>> +
>> + if (elf)
>> + elf_end(elf);
>> + if (fd)
>> + close(fd);
>> + return vaddr;
>> +}
>> diff --git a/userspace/symbol.h b/userspace/symbol.h
>> new file mode 100644
>> index 0000000..478ad2e
>> --- /dev/null
>> +++ b/userspace/symbol.h
>> @@ -0,0 +1,32 @@
>> +/*
>> + * symbol.h
>> + *
>> + * This file is part of ktap by Jovi Zhangwei.
>> + *
>> + * Copyright (C) 2013 Azat Khuzhin <a3at.mail@xxxxxxxxx>.
>> + *
>> + * ktap is free software; you can redistribute it and/or modify it
>> + * under the terms and conditions of the GNU General Public License,
>> + * version 2, as published by the Free Software Foundation.
>> + *
>> + * ktap is distributed in the hope it will be useful, but WITHOUT
>> + * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
>> + * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public
License for
>> + * more details.
>> + *
>> + * You should have received a copy of the GNU General Public License
along with
>> + * this program; if not, write to the Free Software Foundation, Inc.,
>> + * 51 Franklin St - Fifth Floor, Boston, MA 02110-1301 USA.
>> + */
>> +
>> +#include <gelf.h> // GElf_Addr
>> +
>> +
>> +typedef GElf_Addr vaddr_t;
>> +
>> +/**
>> + * Find symbol in DSO
>> + *
>> + * @return 0 on failure, otherwise address of symbol.
>> + */
>> +vaddr_t find_symbol(const char *exec, const char *symbol);
>> --
>> 1.8.4.rc3
>>
>>
>
>
>
> --
> Sincerely,
> Yicheng Qin
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