Index: lld/ELF/Writer.cpp
===================================================================
--- lld/ELF/Writer.cpp
+++ lld/ELF/Writer.cpp
@@ -70,6 +70,7 @@
                          unsigned pFlags);
   void assignFileOffsets();
   void assignFileOffsetsBinary();
+  void reassignPhdrBoundaries();
   void setPhdrs(Partition &part);
   void checkSections();
   void fixSectionAlignments();
@@ -551,6 +552,8 @@
   else
     assignFileOffsetsBinary();
 
+  reassignPhdrBoundaries();
+
   for (Partition &part : partitions)
     setPhdrs(part);
 
@@ -2554,6 +2557,20 @@
     }
 }
 
+template <class ELFT> void Writer<ELFT>::reassignPhdrBoundaries() {
+  // Based on the offsets, update the program headers to generate the correct
+  // size fields afterward. If we don't do this update, out-of-order output
+  // sections can lead to wrong/overflowed size values.
+  for (OutputSection *sec : outputSections) {
+    if (PhdrEntry *ptLoad = sec->ptLoad) {
+      if (OutputSection *first = ptLoad->firstSec)
+        ptLoad->firstSec = (first->addr > sec->addr) ? sec : first;
+      if (OutputSection *last = ptLoad->lastSec)
+        ptLoad->lastSec = (last->addr < sec->addr) ? sec : last;
+    }
+  }
+}
+
 static std::string rangeToString(uint64_t addr, uint64_t len) {
   return "[0x" + utohexstr(addr) + ", 0x" + utohexstr(addr + len - 1) + "]";
 }
Index: lld/test/ELF/out-of-order-sections.s
===================================================================
--- /dev/null
+++ lld/test/ELF/out-of-order-sections.s
@@ -0,0 +1,58 @@
+# REQUIRES: x86
+# RUN: rm -rf %t && split-file %s %t
+# RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %t/c.s -o %c.o
+# RUN: ld.lld --script %t/lda %c.o -o %t/la.o 2>&1
+# RUN: ld.lld --script %t/ldb %c.o -o %t/lb.o 2>&1
+# RUN: llvm-readelf %t/la.o -l 2>&1 | FileCheck --check-prefix=TEST-ORDER-A %s
+# RUN: llvm-readelf %t/lb.o -l 2>&1 | FileCheck --check-prefix=TEST-ORDER-B %s
+
+# TEST-ORDER-A: Elf file type is EXEC (Executable file)
+# TEST-ORDER-A: Entry point 0x10000001
+# TEST-ORDER-A: There are 2 program headers, starting at offset 64
+# TEST-ORDER-A: Program Headers:
+# TEST-ORDER-A:   Type           Offset   VirtAddr           PhysAddr           FileSiz  MemSiz   Flg Align
+# TEST-ORDER-A:   LOAD           0x001000 0x0000000010000000 0x0000000010000000 0x000054 0x000054 R E 0x1000
+# TEST-ORDER-A:   GNU_STACK      0x000000 0x0000000000000000 0x0000000000000000 0x000000 0x000000 RW  0x0
+# TEST-ORDER-A:  Section to Segment mapping:
+# TEST-ORDER-A:   Segment Sections...
+# TEST-ORDER-A:    00     first_section second_section
+
+# TEST-ORDER-B: Elf file type is EXEC (Executable file)
+# TEST-ORDER-B: Entry point 0x10000001
+# TEST-ORDER-B: There are 2 program headers, starting at offset 64
+# TEST-ORDER-B: Program Headers:
+# TEST-ORDER-B:   Type           Offset   VirtAddr           PhysAddr           FileSiz  MemSiz   Flg Align
+# TEST-ORDER-B:   LOAD           0x001000 0x0000000010000000 0x0000000010000000 0x000054 0x000054 R E 0x1000
+# TEST-ORDER-B:   GNU_STACK      0x000000 0x0000000000000000 0x0000000000000000 0x000000 0x000000 RW  0x0
+# TEST-ORDER-B:  Section to Segment mapping:
+# TEST-ORDER-B:   Segment Sections...
+# TEST-ORDER-B:    00     second_section first_section
+
+
+#--- lda
+SECTIONS {
+  first_section 0x10000000 : { KEEP (*(.first_in_section)); } > mem
+  second_section (0x10000000 +64) : { KEEP (*(.second_in_section)); } > mem
+  /DISCARD/ : { KEEP (*(.text, data .comment, .symtab, .strtab)); }
+}
+
+MEMORY { mem (r): org = 0x10000000, len = 0x00100000 }
+
+#--- ldb
+SECTIONS {
+  second_section (0x10000000 +64) : { KEEP (*(.second_in_section)); } > mem
+  first_section 0x10000000 : { KEEP (*(.first_in_section)); } > mem
+  /DISCARD/ : { KEEP (*(.text, data .comment, .symtab, .strtab)); }
+}
+
+MEMORY { mem (r): org = 0x10000000, len = 0x00100000 }
+
+#--- c.s
+.section data,"wa",@nobits
+.zero 1
+.section .second_in_section,"ax",@progbits
+.zero 20
+.section .first_in_section,"ax",@progbits
+.zero 1
+.globl _start
+_start: