From 5ea3d60db1793c81a1bbbd957fe87184e8d1b7ab Mon Sep 17 00:00:00 2001
From: Ben Noordhuis <info@bnoordhuis.nl>
Date: Tue, 28 Jan 2020 11:01:32 +0100
Subject: [PATCH] src: use __executable_start for linux hugepages

`__executable_start` is provided by GNU's and LLVM's default linker
scripts, obviating the need to plug in a custom linker script.

The problem with our bespoke linker script is that it works with ld.bfd
but not ld.gold and cannot easily be ported because the latter linker
doesn't understand the `INSERT BEFORE` directive.

The /proc/self/maps scanner is updated to account for the fact that
there are a number of sections between `&__executable_start` and
the start of the .text section.

Fortunately, those sections are all mapped into the same memory segment
so we only need to look at the next line to find the start of our text
segment.

Fixes: https://github.com/nodejs/node/issues/31520

Backport-PR-URL: https://github.com/nodejs/node/pull/32092
PR-URL: https://github.com/nodejs/node/pull/31547
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Gus Caplan <me@gus.host>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: David Carlier <devnexen@gmail.com>
---
 node.gyp                               |  3 +-
 node.gypi                              | 16 -----
 src/large_pages/ld.implicit.script     | 10 ----
 src/large_pages/ld.implicit.script.lld |  3 -
 src/large_pages/node_large_page.cc     | 83 ++++++++++++++------------
 5 files changed, 47 insertions(+), 68 deletions(-)
 delete mode 100644 src/large_pages/ld.implicit.script
 delete mode 100644 src/large_pages/ld.implicit.script.lld

diff --git a/node.gyp b/node.gyp
index 6f0a95781ef67f..7b80676e4368d8 100644
--- a/node.gyp
+++ b/node.gyp
@@ -854,7 +854,8 @@
           ],
         }],
         [ 'OS in "linux freebsd mac" and '
-          'target_arch=="x64"', {
+          'target_arch=="x64" and '
+          'node_target_type=="executable"', {
           'defines': [ 'NODE_ENABLE_LARGE_CODE_PAGES=1' ],
           'sources': [
             'src/large_pages/node_large_page.cc',
diff --git a/node.gypi b/node.gypi
index a22800af0903ce..116c1c7149425b 100644
--- a/node.gypi
+++ b/node.gypi
@@ -317,22 +317,6 @@
       'ldflags': [ '-Wl,-z,relro',
                    '-Wl,-z,now' ]
     }],
-    [ 'OS=="linux" and '
-      'target_arch=="x64" and '
-      'llvm_version=="0.0"', {
-      'ldflags': [
-        '-Wl,-T',
-        '<!(echo "$(pwd)/src/large_pages/ld.implicit.script")',
-      ]
-    }],
-    [ 'OS=="linux" and '
-      'target_arch=="x64" and '
-      'llvm_version!="0.0"', {
-      'ldflags': [
-        '-Wl,-T',
-        '<!(echo "$(pwd)/src/large_pages/ld.implicit.script.lld")',
-      ]
-    }],
     [ 'node_use_openssl=="true"', {
       'defines': [ 'HAVE_OPENSSL=1' ],
       'conditions': [
diff --git a/src/large_pages/ld.implicit.script b/src/large_pages/ld.implicit.script
deleted file mode 100644
index 7f12e4bd7df9e5..00000000000000
--- a/src/large_pages/ld.implicit.script
+++ /dev/null
@@ -1,10 +0,0 @@
-  SECTIONS {
-    .lpstub            : {
-       *libc.a:*(.text .text.*)
-       *(.lpstub)
-     }
-  }
-  PROVIDE (__nodetext = .);
-  PROVIDE (_nodetext = .);
-  PROVIDE (nodetext = .);
-  INSERT BEFORE .text;
diff --git a/src/large_pages/ld.implicit.script.lld b/src/large_pages/ld.implicit.script.lld
deleted file mode 100644
index b85510bcf07eeb..00000000000000
--- a/src/large_pages/ld.implicit.script.lld
+++ /dev/null
@@ -1,3 +0,0 @@
-  PROVIDE (__nodetext = .);
-  PROVIDE (_nodetext = .);
-  PROVIDE (nodetext = .);
diff --git a/src/large_pages/node_large_page.cc b/src/large_pages/node_large_page.cc
index 252ccba15780d6..ce58e32e719bc8 100644
--- a/src/large_pages/node_large_page.cc
+++ b/src/large_pages/node_large_page.cc
@@ -65,7 +65,11 @@
 // Use madvise with MADV_HUGEPAGE to use Anonymous 2M Pages
 // If successful copy the code there and unmap the original region.
 
-extern char __nodetext;
+#if defined(__linux__)
+extern "C" {
+extern char __executable_start;
+}  // extern "C"
+#endif  // defined(__linux__)
 
 namespace node {
 
@@ -116,17 +120,6 @@ static struct text_region FindNodeTextRegion() {
     return nregion;
   }
 
-  std::string exename;
-  {
-      char selfexe[PATH_MAX];
-
-      size_t size = sizeof(selfexe);
-      if (uv_exepath(selfexe, &size))
-        return nregion;
-
-      exename = std::string(selfexe, size);
-  }
-
   while (std::getline(ifs, map_line)) {
     std::istringstream iss(map_line);
     iss >> std::hex >> start;
@@ -136,26 +129,42 @@ static struct text_region FindNodeTextRegion() {
     iss >> offset;
     iss >> dev;
     iss >> inode;
-    if (inode != 0) {
-      std::string pathname;
-      iss >> pathname;
-      if (pathname == exename && permission == "r-xp") {
-        uintptr_t ntext = reinterpret_cast<uintptr_t>(&__nodetext);
-        if (ntext >= start && ntext < end) {
-          char* from = reinterpret_cast<char*>(hugepage_align_up(ntext));
-          char* to = reinterpret_cast<char*>(hugepage_align_down(end));
-
-          if (from < to) {
-            size_t size = to - from;
-            nregion.found_text_region = true;
-            nregion.from = from;
-            nregion.to = to;
-            nregion.total_hugepages = size / hps;
-          }
-          break;
-        }
-      }
-    }
+
+    if (inode == 0)
+      continue;
+
+    std::string pathname;
+    iss >> pathname;
+
+    if (start != reinterpret_cast<uintptr_t>(&__executable_start))
+      continue;
+
+    // The next line is our .text section.
+    if (!std::getline(ifs, map_line))
+      break;
+
+    iss = std::istringstream(map_line);
+    iss >> std::hex >> start;
+    iss >> dash;
+    iss >> std::hex >> end;
+    iss >> permission;
+
+    if (permission != "r-xp")
+      break;
+
+    char* from = reinterpret_cast<char*>(hugepage_align_up(start));
+    char* to = reinterpret_cast<char*>(hugepage_align_down(end));
+
+    if (from >= to)
+      break;
+
+    size_t size = to - from;
+    nregion.found_text_region = true;
+    nregion.from = from;
+    nregion.to = to;
+    nregion.total_hugepages = size / hps;
+
+    break;
   }
 
   ifs.close();
@@ -408,14 +417,12 @@ int MapStaticCodeToLargePages() {
     return -1;
   }
 
-#if defined(__linux__) || defined(__FreeBSD__)
-  if (r.from > reinterpret_cast<void*>(&MoveTextRegionToLargePages))
-    return MoveTextRegionToLargePages(r);
+#if defined(__FreeBSD__)
+  if (r.from < reinterpret_cast<void*>(&MoveTextRegionToLargePages))
+    return -1;
+#endif
 
-  return -1;
-#elif defined(__APPLE__)
   return MoveTextRegionToLargePages(r);
-#endif
 }
 
 bool IsLargePagesEnabled() {