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@jeremy-w jeremy-w/dump-header-map.c
Last active Oct 13, 2018

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//cc -Wextra -o build/dump-header-map dump-header-map.c
// see: https://github.com/llvm-mirror/clang/blob/release_40/include/clang/Lex/HeaderMapTypes.h
// https://github.com/llvm-mirror/clang/blob/release_40/include/clang/Lex/HeaderMap.h// https://github.com/llvm-mirror/clang/blob/release_40/lib/Lex/HeaderMap.cpp
// This is basically dump() from there.
#include <stdio.h>
#include <stdlib.h>
#include <sysexits.h>
#include <err.h>
#include <fcntl.h>
#include <stdbool.h>
#include <inttypes.h>
#include <sys/types.h>
#include <sys/uio.h>
#include <unistd.h>
#include <assert.h>
#include <sys/mman.h>
#include <sys/stat.h>
enum {
HMAP_HeaderMagicNumber = ('h' << 24) | ('m' << 16) | ('a' << 8) | 'p',
HMAP_HeaderVersion = 0x0001,
HMAP_EmptyBucketKey = 0,
HMAP_SwappedMagic = ('h' << 0) | ('m' << 8) | ('a' << 16) | ('p' << 24),
HMAP_SwappedVersion = 0x0100,
};
struct HMapBucket {
uint32_t Key; // Offset (into strings) of key.
uint32_t Prefix; // Offset (into strings) of value prefix.
uint32_t Suffix; // Offset (into strings) of value suffix.
};
struct HMapHeader {
uint32_t Magic; // Magic word, also indicates byte order.
uint16_t Version; // Version number -- currently 1.
uint16_t Reserved; // Reserved for future use - zero for now.
uint32_t StringsOffset; // Offset to start of string pool.
uint32_t NumEntries; // Number of entries in the string table.
uint32_t NumBuckets; // Number of buckets (always a power of 2).
uint32_t MaxValueLength; // Length of longest result path (excluding nul).
// An array of 'NumBuckets' HMapBucket objects follows this header.
// Strings follow the buckets, at StringsOffset.
};
uint32_t nop_swap(uint32_t);
uint32_t actually_swap(uint32_t);
void dump(const char *path);
int
main(int argc, const char *argv[])
{
assert(actually_swap(HMAP_HeaderMagicNumber) == HMAP_SwappedMagic
&& "failed to properly swap things :(");
if (argc < 2) {
fprintf(
stderr,
"usage: %s HMAP_FILE [HMAP_FILE...]\n\n"
"Dump clang headermap (.hmap file) contents.\n\n"
"See: https://github.com/llvm-mirror/clang/blob/release_40/include/clang/Lex/HeaderMapTypes.h\n"
"and related files\n",
getprogname());
return EX_USAGE;
}
for (int i = 1; i < argc; ++i) {
dump(argv[i]);
putchar('\n');
}
return EXIT_SUCCESS;
}
void
dump(const char *path)
{
int fd = open(path, O_RDONLY|O_CLOEXEC);
if (fd < 0) {
warn(/*EX_NOINPUT,*/ "%s: cannot open", path);
return;
}
struct HMapHeader header;
ssize_t nread = read(fd, &header, sizeof(header));
if (nread < 0) {
warn(/*EX_IOERR,*/ "%s: failed to read header", path);
(void)close(fd);
return;
} else if ((size_t)nread < sizeof(header)) {
warn(
/*EX_DATAERR,*/
"%s: short read: expected %zu bytes, read only %zd",
path, sizeof(header), nread);
(void)close(fd);
return;
}
bool is_swapped = false;
uint32_t (*swap)(uint32_t) = nop_swap;
if (header.Magic == HMAP_HeaderMagicNumber
&& header.Version == HMAP_HeaderVersion) {
is_swapped = false;
} else if (header.Magic == HMAP_SwappedMagic
&& header.Version == HMAP_SwappedVersion) {
is_swapped = true;
swap = actually_swap;
} else {
warn(/*EX_DATAERR,*/ "header lacks HMAP magic");
(void)close(fd);
return;
}
const uint32_t bucket_count = swap(header.NumBuckets);
printf("Header map: %s\n"
"\tHash bucket count: %" PRIu32 "\n"
"\tString table entry count: %" PRIu32 "\n"
"\tMax value length: %" PRIu32 " bytes\n",
path,
bucket_count,
swap(header.NumEntries),
swap(header.MaxValueLength));
struct stat stat;
int stat_err = fstat(fd, &stat);
if (stat_err) {
warn("%s: fstat failed; cannot dump buckets", path);
(void)close(fd);
return;
}
off_t hmap_length = stat.st_size;
const void *hmap = mmap(0, hmap_length, PROT_READ, MAP_FILE|MAP_PRIVATE, fd, 0 /*offset*/);
(void)close(fd);
if (MAP_FAILED == hmap) {
warn("%s: failed to mmap; cannot dump buckets", path);
return;
}
const char *raw = hmap;
const struct HMapBucket *const buckets = (void *)(raw
+ sizeof(struct HMapHeader));
const char *const string_table = (raw
+ sizeof(struct HMapHeader)
+ bucket_count*sizeof(struct HMapBucket));
for (uint32_t i = 0; i < bucket_count; ++i) {
const struct HMapBucket *const bucket = &buckets[i];
if (swap(bucket->Key) == HMAP_EmptyBucketKey) { continue; }
// LLVM is careful to sanity-check bucket-count and strlen,
// but we're just going to assume they're all NUL-terminated
// and not maliciously crafted input files.
//
// This is naive, but this is also not exactly "production" code.
const char *key = string_table + swap(bucket->Key);
const char *prefix = string_table + swap(bucket->Prefix);
const char *suffix = string_table + swap(bucket->Suffix);
printf("\t- Bucket %" PRIu32 ": "
"Key %s -> Prefix %s, Suffix %s\n",
i,
key, prefix, suffix);
}
}
uint32_t
nop_swap(uint32_t u)
{
return u;
}
uint32_t
actually_swap(uint32_t u)
{
uint32_t n = (
((u & 0xFF) << 24)
| ((u & 0xFF00) << 8)
| ((u & 0xFF0000) >> 8)
| ((u & 0xFF000000) >> 24)
);
return n;
}
@jeremy-w

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commented Feb 17, 2017

Example output:

./build/dump-header-map /Users/jeremy/Library/Developer/Xcode/DerivedData/ImportSwift-fvxpitolsctgjmemgmjamfehgmaf/Build/Intermediates/ImportSwift.build/Debug-iphonesimulator/ImportSwift.build/*.hmap
Header map: /Users/jeremy/Library/Developer/Xcode/DerivedData/ImportSwift-fvxpitolsctgjmemgmjamfehgmaf/Build/Intermediates/ImportSwift.build/Debug-iphonesimulator/ImportSwift.build/ImportSwift-all-non-framework-target-headers.hmap
        Hash bucket count: 128
        String table entry count: 0
        Max value length: 0 bytes

Header map: /Users/jeremy/Library/Developer/Xcode/DerivedData/ImportSwift-fvxpitolsctgjmemgmjamfehgmaf/Build/Intermediates/ImportSwift.build/Debug-iphonesimulator/ImportSwift.build/ImportSwift-all-target-headers.hmap
        Hash bucket count: 128
        String table entry count: 0
        Max value length: 0 bytes

Header map: /Users/jeremy/Library/Developer/Xcode/DerivedData/ImportSwift-fvxpitolsctgjmemgmjamfehgmaf/Build/Intermediates/ImportSwift.build/Debug-iphonesimulator/ImportSwift.build/ImportSwift-generated-files.hmap
        Hash bucket count: 8
        String table entry count: 0
        Max value length: 0 bytes

Header map: /Users/jeremy/Library/Developer/Xcode/DerivedData/ImportSwift-fvxpitolsctgjmemgmjamfehgmaf/Build/Intermediates/ImportSwift.build/Debug-iphonesimulator/ImportSwift.build/ImportSwift-own-target-headers.hmap
        Hash bucket count: 128
        String table entry count: 0
        Max value length: 0 bytes

Header map: /Users/jeremy/Library/Developer/Xcode/DerivedData/ImportSwift-fvxpitolsctgjmemgmjamfehgmaf/Build/Intermediates/ImportSwift.build/Debug-iphonesimulator/ImportSwift.build/ImportSwift-project-headers.hmap
        Hash bucket count: 128
        String table entry count: 1
        Max value length: 63 bytes
        - Bucket 106: Key AppDelegate.h -> Prefix /Users/jeremy/Workpad/BNR/ImportSwift/ImportSwift/, Suffix AppDelegate.h

Header map: /Users/jeremy/Library/Developer/Xcode/DerivedData/ImportSwift-fvxpitolsctgjmemgmjamfehgmaf/Build/Intermediates/ImportSwift.build/Debug-iphonesimulator/ImportSwift.build/ImportSwift.hmap
        Hash bucket count: 128
        String table entry count: 1
        Max value length: 63 bytes
        - Bucket 106: Key AppDelegate.h -> Prefix /Users/jeremy/Workpad/BNR/ImportSwift/ImportSwift/, Suffix AppDelegate.h
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