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 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

diff --git a/src/backend/meson.build b/src/backend/meson.build
index fec9f1d03b40f236d5548ff5edcac0f3e52ea894..4f5292d8f88431e945655bf1d30ba7720f1a21bc 100644 (file)
--- 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 24e8f37f634caaac2e471bad476863b4b13fb70e..0d0bf0f6aa59babe8458ec41d7be0c253911e476 100644 (file)
--- a/src/backend/utils/error/elog.c
+++ b/src/backend/utils/error/elog.c
@@ -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
  *