[libc][bazel] Mark socket functions weak

[michaelrj-google]

Downstream ther'es a user that needs the syscall wrappers to be weak. I
intend to set up a proper mechanism for just listing which functions
should be weak eventually, but for now this is necessary.

[llvmbot]

@llvm/pr-subscribers-libc

Author: Michael Jones (michaelrj-google)

Changes

Downstream ther'es a user that needs the syscall wrappers to be weak. I
intend to set up a proper mechanism for just listing which functions
should be weak eventually, but for now this is necessary.

---

Full diff: https://github.com/llvm/llvm-project/pull/115088.diff

1 Files Affected:

• (modified) utils/bazel/llvm-project-overlay/libc/BUILD.bazel (+8)

diff --git a/utils/bazel/llvm-project-overlay/libc/BUILD.bazel b/utils/bazel/llvm-project-overlay/libc/BUILD.bazel
index f6648c9bffa730..089592bc0bc17c 100644
--- a/utils/bazel/llvm-project-overlay/libc/BUILD.bazel
+++ b/utils/bazel/llvm-project-overlay/libc/BUILD.bazel
@@ -4650,6 +4650,7 @@ libc_function(
     name = "socket",
     srcs = ["src/sys/socket/linux/socket.cpp"],
     hdrs = ["src/sys/socket/socket.h"],
+    weak = True,
     deps = [
         ":__support_common",
         ":__support_osutil_syscall",
@@ -4661,6 +4662,7 @@ libc_function(
     name = "socketpair",
     srcs = ["src/sys/socket/linux/socketpair.cpp"],
     hdrs = ["src/sys/socket/socketpair.h"],
+    weak = True,
     deps = [
         ":__support_common",
         ":__support_osutil_syscall",
@@ -4672,6 +4674,7 @@ libc_function(
     name = "send",
     srcs = ["src/sys/socket/linux/send.cpp"],
     hdrs = ["src/sys/socket/send.h"],
+    weak = True,
     deps = [
         ":__support_common",
         ":__support_osutil_syscall",
@@ -4686,6 +4689,7 @@ libc_function(
     name = "sendto",
     srcs = ["src/sys/socket/linux/sendto.cpp"],
     hdrs = ["src/sys/socket/sendto.h"],
+    weak = True,
     deps = [
         ":__support_common",
         ":__support_osutil_syscall",
@@ -4700,6 +4704,7 @@ libc_function(
     name = "sendmsg",
     srcs = ["src/sys/socket/linux/sendmsg.cpp"],
     hdrs = ["src/sys/socket/sendmsg.h"],
+    weak = True,
     deps = [
         ":__support_common",
         ":__support_osutil_syscall",
@@ -4713,6 +4718,7 @@ libc_function(
     name = "recv",
     srcs = ["src/sys/socket/linux/recv.cpp"],
     hdrs = ["src/sys/socket/recv.h"],
+    weak = True,
     deps = [
         ":__support_common",
         ":__support_osutil_syscall",
@@ -4727,6 +4733,7 @@ libc_function(
     name = "recvfrom",
     srcs = ["src/sys/socket/linux/recvfrom.cpp"],
     hdrs = ["src/sys/socket/recvfrom.h"],
+    weak = True,
     deps = [
         ":__support_common",
         ":__support_osutil_syscall",
@@ -4741,6 +4748,7 @@ libc_function(
     name = "recvmsg",
     srcs = ["src/sys/socket/linux/recvmsg.cpp"],
     hdrs = ["src/sys/socket/recvmsg.h"],
+    weak = True,
     deps = [
         ":__support_common",
         ":__support_osutil_syscall",

[vonosmas]

We also define weak = True for various non-syscall wrappers, such as memset, memcmp, etc.

Is there any reason why we shouldn't just define all libc functions as "weak"? Would this mean that in static link mode we allow the user to provide their own implementations / wrappers / proxies of libc functions? (they would also be able to call real implementations by calling a namespace-d version, I think?)

[nickdesaulniers]

Is there any reason why we shouldn't just define all libc functions as "weak"?

Note that declaring a function as having weak linkage is an optimization barrier that inhibits inter-proceedural optimizations such as inlining and constant propagation. If downstream users ever hope to LTO llvm-libc, then marking everything as weak will prevent such optimizations.

[vonosmas]

Right, I agree with Nick's comment that we probably don't want to blanket-define all functions as weak. I do think we need to let Bazel build downstream users decide which functions should be made weak, however -- but let's postpone this update to libc_function logic to future changes. OK with this for now.