libbacktrace: add notes about dl_iterate_phdr to README

	* README: Add notes about dl_iterate_phdr.

1 files changed, 11 insertions, 1 deletions

diff --git a/libbacktrace/README b/libbacktrace/README
index 6225f92..6e6ec33 100644
--- a/libbacktrace/README
+++ b/libbacktrace/README
@@ -5,8 +5,18 @@ The libbacktrace library may be linked into a program or library and
 used to produce symbolic backtraces.
 Sample uses would be to print a detailed backtrace when an error
 occurs or to gather detailed profiling information.
+
 In general the functions provided by this library are async-signal-safe,
 meaning that they may be safely called from a signal handler.
+That said, on systems that use dl_iterate_phdr, such as GNU/Linux,
+the first call to a libbacktrace function will call dl_iterate_phdr,
+which is not in general async-signal-safe.  Therefore, programs
+that call libbacktrace from a signal handler should ensure that they
+make an initial call from outside of a signal handler.
+Similar considerations apply when arranging to call libbacktrace
+from within malloc; dl_iterate_phdr can also call malloc,
+so make an initial call to a libbacktrace function outside of
+malloc before trying to call libbacktrace functions within malloc.
 
 The libbacktrace library is provided under a BSD license.
 See the source files for the exact license text.
@@ -20,7 +30,7 @@ will work.
 See the source file backtrace-supported.h.in for the macros that it
 defines.
 
-As of October 2020, libbacktrace supports ELF, PE/COFF, Mach-O, and
+As of July 2024, libbacktrace supports ELF, PE/COFF, Mach-O, and
 XCOFF executables with DWARF debugging information.
 In other words, it supports GNU/Linux, *BSD, macOS, Windows, and AIX.
 The library is written to make it straightforward to add support for