From a1666e89d771c036df71fc70155ce706114657d8 Mon Sep 17 00:00:00 2001 From: Bryan Green Date: Sat, 1 Nov 2025 23:04:24 -0600 Subject: [PATCH v8] Add backtrace support for Windows using DbgHelp API 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 Unicode 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 from Unicode, 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 Reviewed-by: Euler Taveira Reviewed-by: Jakub Wartak Reviewed-by: Greg Burd Discussion: https://postgr.es/m/a692c0fe-caca-4c08-9c5d-debfd0ef2504@gmail.com --- src/backend/meson.build | 6 ++ src/backend/utils/error/elog.c | 153 ++++++++++++++++++++++++++++++++- 2 files changed, 156 insertions(+), 3 deletions(-) diff --git a/src/backend/meson.build b/src/backend/meson.build index 712a857cdb4..9041cde59fd 100644 --- a/src/backend/meson.build +++ b/src/backend/meson.build @@ -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 diff --git a/src/backend/utils/error/elog.c b/src/backend/utils/error/elog.c index cb1c9d85ffe..d406f18f9d7 100644 --- a/src/backend/utils/error/elog.c +++ b/src/backend/utils/error/elog.c @@ -66,6 +66,10 @@ #include #endif +#ifdef _MSC_VER +#include +#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); @@ -1122,6 +1132,13 @@ 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) @@ -1132,12 +1149,12 @@ 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++) @@ -1148,6 +1165,123 @@ 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; + + if (!backtrace_symbols_initialized) + { + backtrace_process = GetCurrentProcess(); + + SymSetOptions(SYMOPT_UNDNAME | + SYMOPT_DEFERRED_LOADS | + SYMOPT_LOAD_LINES | + SYMOPT_FAIL_CRITICAL_ERRORS); + + if (SymInitialize(backtrace_process, NULL, TRUE)) + { + backtrace_symbols_initialized = true; + on_proc_exit(backtrace_cleanup, 0); + } + else + { + appendStringInfo(&errtrace, + "could not initialize symbol handler: error code %lu", + GetLastError()); + edata->backtrace = errtrace.data; + 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) + { + 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) + { + /* 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) + { + 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"); @@ -1156,6 +1290,19 @@ set_backtrace(ErrorData *edata, int num_skip) edata->backtrace = errtrace.data; } +/* + * Cleanup function for DbgHelp resources. + * Called via on_proc_exit() to release resources allocated by SymInitialize(). + */ +pg_attribute_unused() +static void +backtrace_cleanup(int code, Datum arg) +{ +#ifdef _MSC_VER + SymCleanup(backtrace_process); +#endif +} + /* * errmsg_internal --- add a primary error message text to the current error * -- 2.47.3