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Add backtrace support for Windows using DbgHelp API

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Previously, backtrace generation on Windows would return an "unsupported"
message.  With this commit, we rely on CaptureStackBackTrace() to capture
the call stack and the DbgHelp API (SymFromAddrW, SymGetLineFromAddrW64)
for symbol resolution.

Symbol handler initialization (SymInitialize) is performed once per
process and cached.  If initialization fails, the report for it is
returned as the backtrace output.  The symbol handler is cleaned up via
on_proc_exit() to release DbgHelp resources.

The implementation provides symbol names, offsets, and addresses.  When
PDB files are available, it also includes source file names and line
numbers.  Symbol names and file paths are converted from UTF-16 to the
database encoding using wchar2char(), which properly handles both UTF-8
and non-UTF-8 databases on Windows.  When symbol information is
unavailable or encoding conversion fails, it falls back to displaying raw
addresses.

The implementation uses the explicit UTF16 versions of the DbgHelp
functions (SYMBOL_INFOW, SymFromAddrW, IMAGEHLP_LINEW64,
SymGetLineFromAddrW64) rather than the generic versions.  This allows us
to rely on predictable encoding conversion, rather than using the
haphazard ANSI codepage that we'd get otherwise.

DbgHelp is apparently available on all Windows platforms we support, so
there are no version number checks.

Author: Bryan Green <dbryan.green@gmail.com>
Reviewed-by: Euler Taveira <euler@eulerto.com>
Reviewed-by: Jakub Wartak <jakub.wartak@enterprisedb.com>
Reviewed-by: Greg Burd <greg@burd.me>
Discussion: https://postgr.es/m/a692c0fe-caca-4c08-9c5d-debfd0ef2504@gmail.com
This commit is contained in:
Álvaro Herrera 2026-02-24 17:34:56 +01:00
parent dea0812cda
commit 65707ed9af
No known key found for this signature in database
GPG key ID: 1C20ACB9D5C564AE
2 changed files with 184 additions and 3 deletions
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6
src/backend/meson.build
View file

@ -41,6 +41,12 @@ backend_link_args = []
backend_link_depends = []
# On Windows also make the backend depend on dbghelp, for backtrace support
if host_system == 'windows' and cc.get_id() == 'msvc'
backend_build_deps += cc.find_library('dbghelp')
endif
# On windows when compiling with msvc we need to make postgres export all its
# symbols so that extension libraries can use them. For that we need to scan
# the constituting objects and generate a file specifying all the functions as

181
src/backend/utils/error/elog.c
View file

@ -66,6 +66,10 @@
#include <execinfo.h>
#endif
#ifdef _MSC_VER
#include <dbghelp.h>
#endif
#include "access/xact.h"
#include "common/ip.h"
#include "libpq/libpq.h"
@ -140,6 +144,11 @@ static void write_syslog(int level, const char *line);
static void write_eventlog(int level, const char *line, int len);
#endif
#ifdef _MSC_VER
static bool backtrace_symbols_initialized = false;
static HANDLE backtrace_process = NULL;
#endif
/* We provide a small stack of ErrorData records for re-entrant cases */
#define ERRORDATA_STACK_SIZE 5
@ -180,6 +189,7 @@ static void set_stack_entry_location(ErrorData *edata,
const char *funcname);
static bool matches_backtrace_functions(const char *funcname);
static pg_noinline void set_backtrace(ErrorData *edata, int num_skip);
static void backtrace_cleanup(int code, Datum arg);
static void set_errdata_field(MemoryContextData *cxt, char **ptr, const char *str);
static void FreeErrorDataContents(ErrorData *edata);
static int log_min_messages_cmp(const ListCell *a, const ListCell *b);
@ -1124,6 +1134,13 @@ errbacktrace(void)
* specifies how many inner frames to skip. Use this to avoid showing the
* internal backtrace support functions in the backtrace. This requires that
* this and related functions are not inlined.
*
* The implementation is, unsurprisingly, platform-specific:
* - GNU libc and copycats: Uses backtrace() and backtrace_symbols()
* - Windows: Uses CaptureStackBackTrace() with DbgHelp for symbol resolution
* (requires PDB files; falls back to exported functions/raw addresses if
* unavailable)
* - Others (musl libc): unsupported
*/
static void
set_backtrace(ErrorData *edata, int num_skip)
@ -1134,12 +1151,12 @@ set_backtrace(ErrorData *edata, int num_skip)
#ifdef HAVE_BACKTRACE_SYMBOLS
{
void *buf[100];
void *frames[100];
int nframes;
char **strfrms;
nframes = backtrace(buf, lengthof(buf));
strfrms = backtrace_symbols(buf, nframes);
nframes = backtrace(frames, lengthof(frames));
strfrms = backtrace_symbols(frames, nframes);
if (strfrms != NULL)
{
for (int i = num_skip; i < nframes; i++)
@ -1150,6 +1167,144 @@ set_backtrace(ErrorData *edata, int num_skip)
appendStringInfoString(&errtrace,
"insufficient memory for backtrace generation");
}
#elif defined(_MSC_VER)
{
void *frames[100];
int nframes;
char buffer[sizeof(SYMBOL_INFOW) + MAX_SYM_NAME * sizeof(wchar_t)];
PSYMBOL_INFOW psymbol;
/*
* This is arranged so that we don't retry if we happen to fail to
* initialize state on the first attempt in any one process.
*/
if (!backtrace_symbols_initialized)
{
backtrace_symbols_initialized = true;
if (DuplicateHandle(GetCurrentProcess(),
GetCurrentProcess(),
GetCurrentProcess(),
&backtrace_process,
0,
FALSE,
DUPLICATE_SAME_ACCESS) == 0)
{
appendStringInfo(&errtrace,
"could not get process handle for backtrace: error code %lu",
GetLastError());
edata->backtrace = errtrace.data;
return;
}
SymSetOptions(SYMOPT_DEFERRED_LOADS |
SYMOPT_FAIL_CRITICAL_ERRORS |
SYMOPT_LOAD_LINES |
SYMOPT_UNDNAME);
if (!SymInitialize(backtrace_process, NULL, TRUE))
{
CloseHandle(backtrace_process);
backtrace_process = NULL;
appendStringInfo(&errtrace,
"could not initialize symbol handler: error code %lu",
GetLastError());
edata->backtrace = errtrace.data;
return;
}
on_proc_exit(backtrace_cleanup, 0);
}
if (backtrace_process == NULL)
return;
nframes = CaptureStackBackTrace(num_skip, lengthof(frames), frames, NULL);
if (nframes == 0)
{
appendStringInfoString(&errtrace, "zero stack frames captured");
edata->backtrace = errtrace.data;
return;
}
psymbol = (PSYMBOL_INFOW) buffer;
psymbol->MaxNameLen = MAX_SYM_NAME;
psymbol->SizeOfStruct = sizeof(SYMBOL_INFOW);
for (int i = 0; i < nframes; i++)
{
DWORD64 address = (DWORD64) frames[i];
DWORD64 displacement = 0;
BOOL sym_result;
sym_result = SymFromAddrW(backtrace_process,
address,
&displacement,
psymbol);
if (sym_result == TRUE)
{
char symbol_name[MAX_SYM_NAME];
size_t result;
/*
* Convert symbol name from UTF-16 to database encoding using
* wchar2char(), which handles both UTF-8 and non-UTF-8
* databases correctly on Windows.
*/
result = wchar2char(symbol_name, (const wchar_t *) psymbol->Name,
sizeof(symbol_name), NULL);
if (result == (size_t) -1 || result == sizeof(symbol_name))
{
/* Conversion failed, use address only */
appendStringInfo(&errtrace,
"\n[0x%llx]",
(unsigned long long) address);
}
else
{
IMAGEHLP_LINEW64 line;
DWORD line_displacement = 0;
char filename[MAX_PATH];
line.SizeOfStruct = sizeof(IMAGEHLP_LINEW64);
/* Start with the common part: symbol+offset [address] */
appendStringInfo(&errtrace,
"\n%s+0x%llx [0x%llx]",
symbol_name,
(unsigned long long) displacement,
(unsigned long long) address);
/* Try to append line info if available */
if (SymGetLineFromAddrW64(backtrace_process,
address,
&line_displacement,
&line))
{
result = wchar2char(filename, (const wchar_t *) line.FileName,
sizeof(filename), NULL);
if (result != (size_t) -1 && result != sizeof(filename))
{
appendStringInfo(&errtrace,
" [%s:%lu]",
filename,
(unsigned long) line.LineNumber);
}
}
}
}
else
{
appendStringInfo(&errtrace,
"\n[0x%llx] (symbol lookup failed: error code %lu)",
(unsigned long long) address,
GetLastError());
}
}
}
#else
appendStringInfoString(&errtrace,
"backtrace generation is not supported by this installation");
@ -1158,6 +1313,26 @@ set_backtrace(ErrorData *edata, int num_skip)
edata->backtrace = errtrace.data;
}
/*
* Cleanup function for set_backtrace().
*/
pg_attribute_unused()
static void
backtrace_cleanup(int code, Datum arg)
{
#ifdef _MSC_VER
/*
* Currently only used to clean up after SymInitialize. We shouldn't ever
* be called if backtrace_process is NULL, but better be safe.
*/
if (backtrace_process)
{
SymCleanup(backtrace_process);
backtrace_process = NULL;
}
#endif
}
/*
* errmsg_internal --- add a primary error message text to the current error
*