On Sat, Mar 05, 2016 at 10:30:52AM -0700, Stephen Warren wrote: > When running sandbox, the following phases occur, each with different > malloc implementations or behaviors: > > 1) Dynamic linker execution, using the dynamic linker's own malloc() > implementation. This is fully functional. > > 2) After U-Boot's malloc symbol has been hooked into the GOT, but before > any U-Boot code has run. This phase is entirely non-functional, since > U-Boot's gd symbol is NULL and U-Boot's initf_malloc() and > mem_malloc_init() have not been called. > > At least on Ubuntu Xenial, the dynamic linker does make both malloc() and > free() calls during this phase. Currently these free() calls crash since > they dereference gd, which is NULL. > > U-Boot itself makes no use of malloc() during this phase. > > 3) U-Boot execution after gd is set and initf_malloc() has been called. > This is fully functional, albeit via a very simple malloc() > implementation. > > 4) U-Boot execution after mem_malloc_init() has been called. This is fully > functional with a complete malloc() implementation. > > Furthermore, if code that called malloc() during phase 1 calls free() in > phase 3 or later, it is likely that heap corruption will occur, since > U-Boot's malloc implementation will assume the pointer is part of its own > heap, although it isn't. I have not actively observed this happening. > > To prevent phase 2 from happening, this patch makes all of U-Boot's malloc > library public symbols have hidden visibility. This prevents them from > being hooked into the GOT, so only code in the U-Boot binary itself > actually calls them; any other code will call into the standard C library > malloc(). This also avoids the "furthermore" issue mentioned above. > > I have seen references to this GCC pragma in blog posts from 2008, and > RHEL5's ancient gcc appears to accept it fine, so I believe it's quite > safe to use it without checking gcc version. > > Cc: Rabin Vincent <ra...@rab.in> > Signed-off-by: Stephen Warren <swar...@wwwdotorg.org> > Reviewed-by: Tom Rini <tr...@konsulko.com> > Reviewed-by: Simon Glass <s...@chromium.org>
Applied to u-boot/master, thanks! -- Tom
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