From cd3f69c290c76312e7ae568f8a1b9f2b13e87700 Mon Sep 17 00:00:00 2001
From: John Reiser <jreiser@BitWagon.com>
Date: Thu, 31 Aug 2023 13:25:53 -0700
Subject: [PATCH] Explicit write() can subsume ftruncate()

	modified:   stub/src/amd64-linux.elf-so_main.c
	modified:   stub/src/i386-linux.elf-so_main.c
---
 src/stub/src/amd64-linux.elf-so_main.c | 4 ----
 src/stub/src/i386-linux.elf-so_main.c  | 3 ---
 2 files changed, 7 deletions(-)

diff --git a/src/stub/src/amd64-linux.elf-so_main.c b/src/stub/src/amd64-linux.elf-so_main.c
index 2fb99266..260bba6c 100644
--- a/src/stub/src/amd64-linux.elf-so_main.c
+++ b/src/stub/src/amd64-linux.elf-so_main.c
@@ -263,7 +263,6 @@ make_hatch_x86_64(
         }
         else { // Does not fit at hi end of .text, so must use a new page "permanently"
             int mfd = memfd_create(addr_string("upx"), 0);  // the directory entry
-            ftruncate(mfd, 6);
             Pwrite(mfd, addr_string("\x0f\x05\x5f\x5e\x5a\xc3"), 6);
             hatch = Pmap(0, 6, PROT_READ|PROT_EXEC, MAP_SHARED, mfd, 0);
             close(mfd);
@@ -306,7 +305,6 @@ make_hatch_ppc64(
         }
         else { // Does not fit at hi end of .text, so must use a new page "permanently"
             int mfd = memfd_create(addr_string("upx"), 0);  // the directory entry
-            ftruncate(mfd,sizeof(code));
             Pwrite(mfd, code, sizeof(code));
             hatch = Pmap(0, sizeof(code), PROT_READ|PROT_EXEC, MAP_SHARED, mfd, 0);
             close(mfd);
@@ -345,7 +343,6 @@ make_hatch_arm64(
         }
         else { // Does not fit at hi end of .text, so must use a new page "permanently"
             int mfd = memfd_create(addr_string("upx"), 0);  // the directory entry
-            ftruncate(mfd, sizeof(code));
             Pwrite(mfd, code, sizeof(code));
             void *mfd_addr = Pmap(0, sizeof(code), PROT_READ|PROT_EXEC, MAP_SHARED, mfd, 0);
             close(mfd);
@@ -498,7 +495,6 @@ upx_so_main(  // returns &escape_hatch
     if (phdr->p_flags & PF_X) {
         int mfd = memfd_create(addr_string("upx"), 0);
         unsigned mfd_len = 0ul - PAGE_MASK;
-        ftruncate(mfd, mfd_len);
         Pwrite(mfd, elf_tmp, binfo->sz_unc);  // de-compressed Elf_Ehdr and Elf_Phdrs
         Pwrite(mfd, binfo->sz_unc + va_load, mfd_len - binfo->sz_unc);  // rest of 1st page
 
diff --git a/src/stub/src/i386-linux.elf-so_main.c b/src/stub/src/i386-linux.elf-so_main.c
index a53f682d..bc5d6d91 100644
--- a/src/stub/src/i386-linux.elf-so_main.c
+++ b/src/stub/src/i386-linux.elf-so_main.c
@@ -287,7 +287,6 @@ make_hatch_i386(
         }
         else { // Does not fit at hi end of .text, so must use a new page "permanently"
             int mfd = memfd_create(addr_string("upx"), 0);  // the directory entry
-            //ftruncate(mfd, 4);
             write(mfd, &escape, 4);
             hatch = mmap(0, 4, PROT_READ|PROT_EXEC, MAP_SHARED, mfd, 0);
             close(mfd);
@@ -325,7 +324,6 @@ make_hatch_arm32(
         }
         else { // Does not fit at hi end of .text, so must use a new page "permanently"
             int mfd = memfd_create(addr_string("upx"), 0);  // the directory entry
-            //ftruncate(mfd, 2*4);
             write(mfd, &code, 2*4);
             hatch = Pmap(0, 2*4, PROT_READ|PROT_EXEC, MAP_SHARED, mfd, 0);
             close(mfd);
@@ -555,7 +553,6 @@ upx_so_main(  // returns &escape_hatch
     if (phdr->p_flags & PF_X) {
         int mfd = memfd_create(addr_string("upx"), 0);
         unsigned mfd_len = 0ul - page_mask;
-        ftruncate(mfd, mfd_len);
         Pwrite(mfd, elf_tmp, binfo->sz_unc);  // de-compressed Elf_Ehdr and Elf_Phdrs
         Pwrite(mfd, binfo->sz_unc + va_load, mfd_len - binfo->sz_unc);  // rest of 1st page