[Tarantool-patches] [PATCH luajit v2 1/1] Fix saved bytecode encapsulated in ELF objects.
Sergey Bronnikov
estetus at gmail.com
Tue May 30 11:09:34 MSK 2023
From: Sergey Bronnikov <sergeyb at tarantool.org>
Thanks to Dimitry Andric.
(cherry picked from commit 7dbf0b05f1228c1c719866db5e5f3d58f87f74c8)
Function `bcsave.lua:bcsave_elfobj()` produced an object file in ELF
format with a wrong size size of `.strtab`. Wrong .strtab size causes lld to
show an error message:
```
$ luajit -b -n "module_name" -e "print()" xxx.obj
$ ld.lld xxx.obj
ld.lld: error: xxx.obj: SHT_STRTAB string table section [index 3] is non-null terminated
```
Sergey Bronnikov:
* added the description and the test for the problem
Signed-off-by: Sergey Bronnikov <sergeyb at tarantool.org>
Reviewed-by: Sergey Kaplun <skaplun at tarantool.org>
Reviewed-by: Maxim Kokryashkin <m.kokryashkin at tarantool.org>
---
Changes in v2:
- Fixed comments as per review by Sergey.
Branch: https://github.com/tarantool/luajit/tree/ligurio/gh-366-strtab-section-correct-size
Tarantool CI: https://github.com/ligurio/tarantool/tree/ligurio/gh-xxxx-strtab-section-correct-size
src/jit/bcsave.lua | 2 +-
.../lj-366-strtab-correct-size.test.lua | 202 ++++++++++++++++++
2 files changed, 203 insertions(+), 1 deletion(-)
create mode 100644 test/tarantool-tests/lj-366-strtab-correct-size.test.lua
diff --git a/src/jit/bcsave.lua b/src/jit/bcsave.lua
index c17c88e0..2553d97e 100644
--- a/src/jit/bcsave.lua
+++ b/src/jit/bcsave.lua
@@ -275,7 +275,7 @@ typedef struct {
o.sect[2].size = fofs(ofs)
o.sect[3].type = f32(3) -- .strtab
o.sect[3].ofs = fofs(sofs + ofs)
- o.sect[3].size = fofs(#symname+1)
+ o.sect[3].size = fofs(#symname+2)
ffi.copy(o.space+ofs+1, symname)
ofs = ofs + #symname + 2
o.sect[4].type = f32(1) -- .rodata
diff --git a/test/tarantool-tests/lj-366-strtab-correct-size.test.lua b/test/tarantool-tests/lj-366-strtab-correct-size.test.lua
new file mode 100644
index 00000000..5dec6751
--- /dev/null
+++ b/test/tarantool-tests/lj-366-strtab-correct-size.test.lua
@@ -0,0 +1,202 @@
+local tap = require('tap')
+local test = tap.test('lj-366-strtab-correct-size'):skipcond({
+ -- The test is ELF-specific, and because LuaJIT exports object
+ -- files in ELF format for all operating systems except macOS
+ -- and Windows we skip test on these OSes.
+ -- See src/jit/bcsave.lua:bcsave_obj.
+ ['Disabled on Windows'] = jit.os == 'Windows',
+ ['Disabled on macOS'] = jit.os == 'OSX',
+})
+
+local ffi = require 'ffi'
+
+-- Command below exports bytecode as an object file in ELF format:
+-- $ luajit -b -n 'lango_team' -e 'print()' xxx.obj
+-- $ file xxx.obj
+-- xxx.obj: ELF 64-bit LSB relocatable, x86-64, version 1 (SYSV), not stripped
+--
+-- With read_elf(1) it is possible displaying the entries in symbol table
+-- section of the file, if it has one. Object file contains a single symbol
+-- with name 'luaJIT_BC_lango_team':
+--
+-- $ readelf --symbols xxx.obj
+--
+-- Symbol table '.symtab' contains 2 entries:
+-- Num: Value Size Type Bind Vis Ndx Name
+-- 0: 0000000000000000 0 NOTYPE LOCAL DEFAULT UND
+-- 1: 0000000000000000 66 OBJECT GLOBAL DEFAULT 4 luaJIT_BC_lango_team
+--
+-- and displaying the information contained in the file's section headers, if
+-- it has any. For our purposes we are interesting in section .symtab,
+-- so other sections snipped in the output:
+--
+-- $ readelf --section-headers xxx.obj
+-- There are 6 section headers, starting at offset 0x40:
+--
+-- Section Headers:
+-- [Nr] Name Type Address Offset
+-- Size EntSize Flags Link Info Align
+-- ...
+--
+-- [ 3] .strtab STRTAB 0000000000000000 00000223
+-- 0000000000000016 0000000000000000 0 0 1
+-- ...
+-- Reference numbers for strtab offset and size could be obtained with
+-- readelf(1). Note that number system of these numbers are hexadecimal.
+
+local expected_strtab_size = 0x16
+local expected_strtab_offset = 0x223
+local module_name = 'lango_team'
+
+-- Symbol name prefix for LuaJIT bytecode defined in bcsave.lua.
+local LJBC_PREFIX = 'luaJIT_BC_'
+
+-- Defined in elf.h.
+local SHT_SYMTAB = 2
+
+-- Using the same declarations as defined in <src/jit/bcsave.lua>.
+ffi.cdef[[
+typedef struct {
+ uint8_t emagic[4], eclass, eendian, eversion, eosabi, eabiversion, epad[7];
+ uint16_t type, machine;
+ uint32_t version;
+ uint32_t entry, phofs, shofs;
+ uint32_t flags;
+ uint16_t ehsize, phentsize, phnum, shentsize, shnum, shstridx;
+} ELF32header;
+
+typedef struct {
+ uint8_t emagic[4], eclass, eendian, eversion, eosabi, eabiversion, epad[7];
+ uint16_t type, machine;
+ uint32_t version;
+ uint64_t entry, phofs, shofs;
+ uint32_t flags;
+ uint16_t ehsize, phentsize, phnum, shentsize, shnum, shstridx;
+} ELF64header;
+
+typedef struct {
+ uint32_t name, type, flags, addr, ofs, size, link, info, align, entsize;
+} ELF32sectheader;
+
+typedef struct {
+ uint32_t name, type;
+ uint64_t flags, addr, ofs, size;
+ uint32_t link, info;
+ uint64_t align, entsize;
+} ELF64sectheader;
+
+typedef struct {
+ uint32_t name, value, size;
+ uint8_t info, other;
+ uint16_t sectidx;
+} ELF32symbol;
+
+typedef struct {
+ uint32_t name;
+ uint8_t info, other;
+ uint16_t sectidx;
+ uint64_t value, size;
+} ELF64symbol;
+
+typedef struct {
+ ELF32header hdr;
+ ELF32sectheader sect[6];
+ ELF32symbol sym[2];
+ uint8_t space[4096];
+} ELF32obj;
+
+typedef struct {
+ ELF64header hdr;
+ ELF64sectheader sect[6];
+ ELF64symbol sym[2];
+ uint8_t space[4096];
+} ELF64obj;
+]]
+
+local is64_arch = {
+ ['x64'] = true,
+ ['arm64'] = true,
+ ['arm64be'] = true,
+ ['ppc'] = false,
+ ['mips'] = false,
+}
+
+local is64 = is64_arch[jit.arch] or false
+
+local function create_obj_file(name)
+ local elf_filename = os.tmpname() .. '.obj'
+ local lua_path = os.getenv('LUA_PATH')
+ local lua_bin = require('utils').luacmd(arg):match('%S+')
+ local cmd_fmt = 'LUA_PATH="%s" %s -b -n "%s" -e "print()" %s'
+ local cmd = (cmd_fmt):format(lua_path, lua_bin, name, elf_filename)
+ local ret = os.execute(cmd)
+ assert(ret == 0, 'create an object file')
+ return elf_filename
+end
+
+-- Reads a file located in a specified path and returns its content.
+local function read_file(path)
+ local file = assert(io.open(path), 'cannot open an object file')
+ local content = file:read('*a')
+ file:close()
+ return content
+end
+
+-- Parses a buffer in an ELF format and returns an offset and a size of strtab
+-- and symtab sections.
+local function read_elf(elf_content)
+ local ELFobj_type = ffi.typeof(is64 and 'ELF64obj *' or 'ELF32obj *')
+ local ELFsectheader_type = ffi.typeof(is64 and 'ELF64sectheader *' or 'ELF32sectheader *')
+ local elf = ffi.cast(ELFobj_type, elf_content)
+ local symtab_hdr, strtab_hdr
+ -- Iterate by section headers.
+ for i = 0, elf.hdr.shnum do
+ local sec = ffi.cast(ELFsectheader_type, elf.sect[i])
+ if sec.type == SHT_SYMTAB then
+ symtab_hdr = sec
+ strtab_hdr = ffi.cast(ELFsectheader_type, elf.sect[symtab_hdr.link])
+ break
+ end
+ end
+
+ assert(strtab_hdr ~= nil, 'section .strtab was not found')
+ assert(symtab_hdr ~= nil, 'section .symtab was not found')
+
+ return strtab_hdr, symtab_hdr
+end
+
+test:plan(3)
+
+local elf_filename = create_obj_file(module_name)
+local elf_content = read_file(elf_filename)
+assert(#elf_content ~= 0, 'cannot read an object file')
+
+local strtab, symtab = read_elf(elf_content)
+local strtab_size = tonumber(strtab.size)
+local strtab_offset = tonumber(strtab.ofs)
+local symtab_size = tonumber(symtab.size)
+local sym_cnt = tonumber(symtab_size / symtab.entsize)
+assert(sym_cnt ~= 0, 'number of symbols is zero')
+
+test:is(strtab_size, expected_strtab_size, 'check .strtab size')
+test:is(strtab_offset, expected_strtab_offset, 'check .strtab offset')
+
+local strtab_str = string.sub(elf_content, strtab_offset, strtab_offset + strtab_size)
+
+local strtab_p = ffi.cast('char *', strtab_str)
+local sym_name_expected = LJBC_PREFIX .. module_name
+local sym_is_found = false
+for i = 1, sym_cnt do
+ local sym_name = ffi.string(strtab_p + i)
+ if sym_name_expected == sym_name then
+ sym_is_found = true
+ break
+ end
+end
+
+test:ok(sym_is_found == true, 'symbol is found')
+
+local ret = os.remove(elf_filename)
+assert(ret == true, 'cannot remove an object file')
+
+os.exit(test:check() and 0 or 1)
--
2.34.1
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