1+ /*
2+ * vdso2c - A vdso image preparation tool
3+ * Copyright (c) 2014 Andy Lutomirski and others
4+ * Licensed under the GPL v2
5+ *
6+ * vdso2c requires stripped and unstripped input. It would be trivial
7+ * to fully strip the input in here, but, for reasons described below,
8+ * we need to write a section table. Doing this is more or less
9+ * equivalent to dropping all non-allocatable sections, but it's
10+ * easier to let objcopy handle that instead of doing it ourselves.
11+ * If we ever need to do something fancier than what objcopy provides,
12+ * it would be straightforward to add here.
13+ *
14+ * We're keep a section table for a few reasons:
15+ *
16+ * The Go runtime had a couple of bugs: it would read the section
17+ * table to try to figure out how many dynamic symbols there were (it
18+ * shouldn't have looked at the section table at all) and, if there
19+ * were no SHT_SYNDYM section table entry, it would use an
20+ * uninitialized value for the number of symbols. An empty DYNSYM
21+ * table would work, but I see no reason not to write a valid one (and
22+ * keep full performance for old Go programs). This hack is only
23+ * needed on x86_64.
24+ *
25+ * The bug was introduced on 2012-08-31 by:
26+ * https://code.google.com/p/go/source/detail?r=56ea40aac72b
27+ * and was fixed on 2014-06-13 by:
28+ * https://code.google.com/p/go/source/detail?r=fc1cd5e12595
29+ *
30+ * Binutils has issues debugging the vDSO: it reads the section table to
31+ * find SHT_NOTE; it won't look at PT_NOTE for the in-memory vDSO, which
32+ * would break build-id if we removed the section table. Binutils
33+ * also requires that shstrndx != 0. See:
34+ * https://sourceware.org/bugzilla/show_bug.cgi?id=17064
35+ *
36+ * elfutils might not look for PT_NOTE if there is a section table at
37+ * all. I don't know whether this matters for any practical purpose.
38+ *
39+ * For simplicity, rather than hacking up a partial section table, we
40+ * just write a mostly complete one. We omit non-dynamic symbols,
41+ * though, since they're rather large.
42+ *
43+ * Once binutils gets fixed, we might be able to drop this for all but
44+ * the 64-bit vdso, since build-id only works in kernel RPMs, and
45+ * systems that update to new enough kernel RPMs will likely update
46+ * binutils in sync. build-id has never worked for home-built kernel
47+ * RPMs without manual symlinking, and I suspect that no one ever does
48+ * that.
49+ */
50+
151#include <inttypes.h>
252#include <stdint.h>
353#include <unistd.h>
@@ -20,9 +70,9 @@ const char *outfilename;
2070
2171/* Symbols that we need in vdso2c. */
2272enum {
73+ sym_vvar_start ,
2374 sym_vvar_page ,
2475 sym_hpet_page ,
25- sym_end_mapping ,
2676 sym_VDSO_FAKE_SECTION_TABLE_START ,
2777 sym_VDSO_FAKE_SECTION_TABLE_END ,
2878};
@@ -38,9 +88,9 @@ struct vdso_sym {
3888};
3989
4090struct vdso_sym required_syms [] = {
91+ [sym_vvar_start ] = {"vvar_start" , true},
4192 [sym_vvar_page ] = {"vvar_page" , true},
4293 [sym_hpet_page ] = {"hpet_page" , true},
43- [sym_end_mapping ] = {"end_mapping" , true},
4494 [sym_VDSO_FAKE_SECTION_TABLE_START ] = {
4595 "VDSO_FAKE_SECTION_TABLE_START" , false
4696 },
@@ -61,7 +111,8 @@ static void fail(const char *format, ...)
61111 va_start (ap , format );
62112 fprintf (stderr , "Error: " );
63113 vfprintf (stderr , format , ap );
64- unlink (outfilename );
114+ if (outfilename )
115+ unlink (outfilename );
65116 exit (1 );
66117 va_end (ap );
67118}
@@ -96,9 +147,11 @@ extern void bad_put_le(void);
96147
97148#define NSYMS (sizeof(required_syms) / sizeof(required_syms[0]))
98149
99- #define BITSFUNC3 (name , bits ) name##bits
100- #define BITSFUNC2 (name , bits ) BITSFUNC3(name, bits)
101- #define BITSFUNC (name ) BITSFUNC2(name, ELF_BITS)
150+ #define BITSFUNC3 (name , bits , suffix ) name##bits##suffix
151+ #define BITSFUNC2 (name , bits , suffix ) BITSFUNC3(name, bits, suffix)
152+ #define BITSFUNC (name ) BITSFUNC2(name, ELF_BITS, )
153+
154+ #define INT_BITS BITSFUNC2(int, ELF_BITS, _t)
102155
103156#define ELF_BITS_XFORM2 (bits , x ) Elf##bits##_##x
104157#define ELF_BITS_XFORM (bits , x ) ELF_BITS_XFORM2(bits, x)
@@ -112,38 +165,61 @@ extern void bad_put_le(void);
112165#include "vdso2c.h"
113166#undef ELF_BITS
114167
115- static void go (void * addr , size_t len , FILE * outfile , const char * name )
168+ static void go (void * raw_addr , size_t raw_len ,
169+ void * stripped_addr , size_t stripped_len ,
170+ FILE * outfile , const char * name )
116171{
117- Elf64_Ehdr * hdr = (Elf64_Ehdr * )addr ;
172+ Elf64_Ehdr * hdr = (Elf64_Ehdr * )raw_addr ;
118173
119174 if (hdr -> e_ident [EI_CLASS ] == ELFCLASS64 ) {
120- go64 (addr , len , outfile , name );
175+ go64 (raw_addr , raw_len , stripped_addr , stripped_len ,
176+ outfile , name );
121177 } else if (hdr -> e_ident [EI_CLASS ] == ELFCLASS32 ) {
122- go32 (addr , len , outfile , name );
178+ go32 (raw_addr , raw_len , stripped_addr , stripped_len ,
179+ outfile , name );
123180 } else {
124181 fail ("unknown ELF class\n" );
125182 }
126183}
127184
185+ static void map_input (const char * name , void * * addr , size_t * len , int prot )
186+ {
187+ off_t tmp_len ;
188+
189+ int fd = open (name , O_RDONLY );
190+ if (fd == -1 )
191+ err (1 , "%s" , name );
192+
193+ tmp_len = lseek (fd , 0 , SEEK_END );
194+ if (tmp_len == (off_t )- 1 )
195+ err (1 , "lseek" );
196+ * len = (size_t )tmp_len ;
197+
198+ * addr = mmap (NULL , tmp_len , prot , MAP_PRIVATE , fd , 0 );
199+ if (* addr == MAP_FAILED )
200+ err (1 , "mmap" );
201+
202+ close (fd );
203+ }
204+
128205int main (int argc , char * * argv )
129206{
130- int fd ;
131- off_t len ;
132- void * addr ;
207+ size_t raw_len , stripped_len ;
208+ void * raw_addr , * stripped_addr ;
133209 FILE * outfile ;
134210 char * name , * tmp ;
135211 int namelen ;
136212
137- if (argc != 3 ) {
138- printf ("Usage: vdso2c INPUT OUTPUT\n" );
213+ if (argc != 4 ) {
214+ printf ("Usage: vdso2c RAW_INPUT STRIPPED_INPUT OUTPUT\n" );
139215 return 1 ;
140216 }
141217
142218 /*
143219 * Figure out the struct name. If we're writing to a .so file,
144220 * generate raw output insted.
145221 */
146- name = strdup (argv [2 ]);
222+ name = strdup (argv [3 ]);
147223 namelen = strlen (name );
148224 if (namelen >= 3 && !strcmp (name + namelen - 3 , ".so" )) {
149225 name = NULL ;
@@ -159,26 +235,18 @@ int main(int argc, char **argv)
159235 * tmp = '_' ;
160236 }
161237
162- fd = open (argv [1 ], O_RDONLY );
163- if (fd == -1 )
164- err (1 , "%s" , argv [1 ]);
165-
166- len = lseek (fd , 0 , SEEK_END );
167- if (len == (off_t )- 1 )
168- err (1 , "lseek" );
169-
170- addr = mmap (NULL , len , PROT_READ | PROT_WRITE , MAP_PRIVATE , fd , 0 );
171- if (addr == MAP_FAILED )
172- err (1 , "mmap" );
238+ map_input (argv [1 ], & raw_addr , & raw_len , PROT_READ );
239+ map_input (argv [2 ], & stripped_addr , & stripped_len , PROT_READ );
173240
174- outfilename = argv [2 ];
241+ outfilename = argv [3 ];
175242 outfile = fopen (outfilename , "w" );
176243 if (!outfile )
177244 err (1 , "%s" , argv [2 ]);
178245
179- go (addr , ( size_t ) len , outfile , name );
246+ go (raw_addr , raw_len , stripped_addr , stripped_len , outfile , name );
180247
181- munmap (addr , len );
248+ munmap (raw_addr , raw_len );
249+ munmap (stripped_addr , stripped_len );
182250 fclose (outfile );
183251
184252 return 0 ;
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