Darwin doc: describe apple pointer area and Massif woes

diff --git a/docs/internals/Darwin-debug.txt b/docs/internals/Darwin-debug.txt
index 705d6d57de5661de709b6b2b099ed8b895afe8a3..e753961c79309df56cc6f7fad836188571f7eb45 100644 (file)
--- a/docs/internals/Darwin-debug.txt
+++ b/docs/internals/Darwin-debug.txt
@@ -59,4 +59,9 @@ DYLD_SHARED_REGION gets set to "avoid" (but note that for macOS 11
 Big Sur and later "avoid" is no longer an option).
 
 The Darwin callstack is a bit simpler to synthesise than the ones on
 Big Sur and later "avoid" is no longer an option).
 
 The Darwin callstack is a bit simpler to synthesise than the ones on

-ELF platforms. There is no auxiliary vector (auxv) to construct.
+ELF platforms. There is no auxiliary vector (auxv) to construct. However,
+there is the "apple pointer area". At present we do not pass anything
+that we get from the loader (and this is something of an omission).
+Instead we just synthesise the small number of entries that we need.
+Mostly these values are only used by dyld and for initialising the
+system libs when they load.

diff --git a/docs/internals/Darwin-notes.txt b/docs/internals/Darwin-notes.txt
index 0cedd16981c09bedfa34312f669f9a95a65b6b1e..0eb93fc92146e117e054d98e70de8b53751cb122 100644 (file)
--- a/docs/internals/Darwin-notes.txt
+++ b/docs/internals/Darwin-notes.txt
@@ -71,6 +71,43 @@ means that I don't know which is the oldest version of macOS that
 will build Valgrind (as of December 2025). Somewhere between 10.8 (Darwin 12)
 and 10.12 (Darwin 16).
 
 will build Valgrind (as of December 2025). Somewhere between 10.8 (Darwin 12)
 and 10.12 (Darwin 16).
 

+Massif on Darwin
+~~~~~~~~~~~~~~~~
+
+There is one fundamental difference in the architecture of Darwin
+compared to the other ELF based systems. To start an ELF executable
+ld.so is used. This is a minimalistic binary that just does the
+loading and runtime link-editing of dependent shared libraries.
+Darwin dyld does roughly the same thing except that it triggers
+much more initialisation. Darwin does not have separate libraries
+for the C and C++ standard libraries. Instead it has libSystem.
+That is more like libc and libstdc++ and the Objective-C lib and
+libcrypto and networking libs and about 30 other libs all bundled
+into one. The result is that even before reaching "main()" a
+Darwin guest will have performed vastly more allocations than
+on an ELF system. For comparison, C++ Hello World on FreeBSD
+does one allocation. On Darwin 22 it does 178 allocations. As
+an aside, many of those are not deallocated, which also makes
+a mess of all of the memcheck leak tests.
+
+All this means that the massif tests need very extensive use
+of --ignore-fn for Darwin. There are hundreds of allocations
+and the allocator functions seem to change frequently between
+Darwin versions. For larger allocations, getting the name
+of the allocation function is just a question of looking at
+the failure diff. For small allocations the function may not
+appear in the detailed reports but still cause a diff in
+the allocation totals. In that case consider trying
+- use --threshold=0.0 --detailed-freq=1
+- rerun the test outside of regtest (you can use the
+  .vgtest.log to get the full command line)
+- if all else fails, run with --trace-malloc=yes to try to
+  find out which allocation function (malloc, calloc etc)
+  corresponds to the unaccounted size and then use gdb
+  and put a breakpoint on that allocation function.
+
+DHAT has similar issues but no --ignore-fn option (yet).
+

 
 Valgrind-developer notes, todos re the MacOSX port
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
 Valgrind-developer notes, todos re the MacOSX port
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~