From c909e7786e36ddd450eaac2d3b5d062a70416638 Mon Sep 17 00:00:00 2001
From: William Woodruff <william@trailofbits.com>
Date: Tue, 29 Jun 2021 13:43:27 -0400
Subject: [PATCH 1/3] README: document LLVM_LINK_FLAGS

---
 README.md | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/README.md b/README.md
index 8c5ed8e..f48c956 100644
--- a/README.md
+++ b/README.md
@@ -29,6 +29,7 @@ bitcode in parallel, and is faster. A comparison between the two tools can be gl
 |  LLVM_COMPILER              | *not supported* (clang only)|
 |  LLVM_GCC_PREFIX            | *not supported* (clang only)|
 |  LLVM_DRAGONEGG_PLUGIN      | *not supported* (clang only)|
+|  LLVM_LINK_FLAGS            | *not supported*             |
 
 
 This project, `gllvm`, provides tools for building whole-program (or
@@ -252,6 +253,11 @@ produces the bitcode. This can be fulfilled by setting the
 `LLVM_BITCODE_GENERATION_FLAGS` environment variable to the desired
 flags, for example `"-flto -fwhole-program-vtables"`.
 
+In other situations it is desirable to pass certain flags to `llvm-link` in the step
+that merges multiple individual bitcode files together (i.e., within `get-bc`).
+This can be fulfilled by setting the `LLVM_LINK_FLAGS` environment variable to
+the desired flags, for example `"-internalize -only-needed"`.
+
 ## Beware of link time optimization.
 
 If the package you are building happens to take advantage of recent `clang` developments 

From b789b6b9cefc52ef2ccce9604714668121ff7463 Mon Sep 17 00:00:00 2001
From: William Woodruff <william@trailofbits.com>
Date: Tue, 29 Jun 2021 13:43:40 -0400
Subject: [PATCH 2/3] shared/environment: scaffolding for LLVM_LINK_FLAGS

---
 shared/environment.go | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/shared/environment.go b/shared/environment.go
index 19891c3..53969b9 100644
--- a/shared/environment.go
+++ b/shared/environment.go
@@ -68,6 +68,9 @@ var LLVMARName string
 //LLVMLINKName is the user configured name of the llvm-link.
 var LLVMLINKName string
 
+//LLVMLINKFlags is the user configured list of flags to append to llvm-link.
+var LLVMLINKFlags []string
+
 //LLVMConfigureOnly is the user configured flag indicating a single pass mode is required.
 var LLVMConfigureOnly string
 
@@ -99,6 +102,7 @@ const (
 	envf       = "LLVM_F_NAME"
 	envar      = "LLVM_AR_NAME"
 	envlnk     = "LLVM_LINK_NAME"
+	envlnkflgs = "LLVM_LINK_FLAGS"
 	envcfg     = "WLLVM_CONFIGURE_ONLY"
 	envbc      = "WLLVM_BC_STORE"
 	envlvl     = "WLLVM_OUTPUT_LEVEL"
@@ -142,6 +146,7 @@ func ResetEnvironment() {
 	LLVMFName = ""
 	LLVMARName = ""
 	LLVMLINKName = ""
+	LLVMLINKFlags = []string{}
 	LLVMConfigureOnly = ""
 	LLVMBitcodeStorePath = ""
 	LLVMLoggingLevel = ""
@@ -160,6 +165,7 @@ func FetchEnvironment() {
 	LLVMFName = os.Getenv(envf)
 	LLVMARName = os.Getenv(envar)
 	LLVMLINKName = os.Getenv(envlnk)
+	LLVMLINKFlags = strings.Fields(os.Getenv(envlnkflgs))
 
 	LLVMConfigureOnly = os.Getenv(envcfg)
 	LLVMBitcodeStorePath = os.Getenv(envbc)

From cd6d58d084a3789730ab2600faaafa8461807b2b Mon Sep 17 00:00:00 2001
From: William Woodruff <william@trailofbits.com>
Date: Tue, 29 Jun 2021 14:04:57 -0400
Subject: [PATCH 3/3] extractor: inject LLVM_LINK_FLAGS

---
 shared/extractor.go | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/shared/extractor.go b/shared/extractor.go
index 9228ba6..27ac672 100644
--- a/shared/extractor.go
+++ b/shared/extractor.go
@@ -661,6 +661,10 @@ func linkBitcodeFilesIncrementally(ea ExtractionArgs, filesToLink []string, argM
 	if ea.Verbose {
 		linkArgs = append(linkArgs, "-v")
 	}
+
+	// Append any custom llvm-link flags requested by the user.
+	// We only do this for the last llvm-link invocation.
+	linkArgs = append(linkArgs, LLVMLINKFlags...)
 	linkArgs = append(linkArgs, tmpFileList...)
 
 	linkArgs = append(linkArgs, "-o", ea.OutputFile)
@@ -682,10 +686,15 @@ func linkBitcodeFiles(ea ExtractionArgs, filesToLink []string) (success bool) {
 	if ea.Verbose {
 		linkArgs = append(linkArgs, "-v")
 	}
+
 	if getsize(filesToLink) > argMax { //command line size too large for the OS (necessitated by chromium)
 		return linkBitcodeFilesIncrementally(ea, filesToLink, argMax, linkArgs)
 	}
 	var err error
+
+	// Append any custom llvm-link flags requested by the user.
+	// N.B. that we do this specially for the incremental link case.
+	linkArgs = append(linkArgs, LLVMLINKFlags...)
 	linkArgs = append(linkArgs, "-o", ea.OutputFile)
 	linkArgs = append(linkArgs, filesToLink...)
 	success, err = execCmd(ea.LlvmLinkerName, linkArgs, "")