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Merge "docs: mention the fact that bionic now uses ifuncs."

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am: 2059021322

Change-Id: I4e64df2e56576a5445b08338ae69e02643ac0db9
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Elliott Hughes 2019-03-26 10:49:32 -07:00 committed by android-build-merger
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android-changes-for-ndk-developers.md
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@ -417,3 +417,17 @@ are possible workarounds.
| No workaround | Works for static STL | Broken | Works |
| `-Wl,-z,nodelete` | Works for static STL | Works | Works |
| No `dlclose` | Works | Works | Works |
## Use of IFUNC in libc (True for all API levels on devices running Q)
Starting with Android Q (API level 29), libc uses
[IFUNC](https://sourceware.org/glibc/wiki/GNU_IFUNC) functionality in
the dynamic linker to choose optimized assembler routines at run time
rather than at build time. This lets us use the same `libc.so` on all
devices, and is similar to what other OSes already did. Because the zygote
uses the C library, this decision is made long before we know what API
level an app targets, so all code sees the new IFUNC-using C library.
Most apps should be unaffected by this change, but apps that hook or try to
detect hooking of C library functions might need to fix their code to cope
with IFUNC relocations. The affected functions are from `<string.h>`, but
may expand to include more functions (and more libraries) in future.