Author: jhb
Date: Fri May  8 14:48:45 2020
New Revision: 360814
URL: https://svnweb.freebsd.org/changeset/base/360814

Log:
  MFC 348611: Expose the kernel's build-ID through sysctl
  
  After our migration (of certain architectures) to lld the kernel is built
  with a unique build-ID.  Make it available via a sysctl and uname(1) to
  allow the user to identify their running kernel.

Modified:
  stable/12/sys/conf/ldscript.amd64
  stable/12/sys/conf/ldscript.arm
  stable/12/sys/conf/ldscript.arm64
  stable/12/sys/conf/ldscript.i386
  stable/12/sys/conf/ldscript.mips
  stable/12/sys/conf/ldscript.mips.cfe
  stable/12/sys/conf/ldscript.mips.mips64
  stable/12/sys/conf/ldscript.mips.octeon1
  stable/12/sys/conf/ldscript.powerpc
  stable/12/sys/conf/ldscript.powerpc64
  stable/12/sys/conf/ldscript.powerpcspe
  stable/12/sys/conf/ldscript.riscv
  stable/12/sys/conf/ldscript.sparc64
  stable/12/sys/kern/kern_mib.c
Directory Properties:
  stable/12/   (props changed)

Modified: stable/12/sys/conf/ldscript.amd64
==============================================================================
--- stable/12/sys/conf/ldscript.amd64   Fri May  8 14:39:38 2020        
(r360813)
+++ stable/12/sys/conf/ldscript.amd64   Fri May  8 14:48:45 2020        
(r360814)
@@ -74,6 +74,11 @@ SECTIONS
   PROVIDE (etext = .);
   .rodata         : { *(.rodata .rodata.* .gnu.linkonce.r.*) }
   .rodata1        : { *(.rodata1) }
+  .note.gnu.build-id : {
+    PROVIDE (__build_id_start = .);
+    *(.note.gnu.build-id)
+    PROVIDE (__build_id_end = .);
+  }
   .eh_frame_hdr : { *(.eh_frame_hdr) }
   .eh_frame       : ONLY_IF_RO { KEEP (*(.eh_frame)) }
   .gcc_except_table   : ONLY_IF_RO { *(.gcc_except_table .gcc_except_table.*) }

Modified: stable/12/sys/conf/ldscript.arm
==============================================================================
--- stable/12/sys/conf/ldscript.arm     Fri May  8 14:39:38 2020        
(r360813)
+++ stable/12/sys/conf/ldscript.arm     Fri May  8 14:48:45 2020        
(r360814)
@@ -27,6 +27,11 @@ SECTIONS
   .gnu.version   : { *(.gnu.version)   }
   .gnu.version_d   : { *(.gnu.version_d)       }
   .gnu.version_r   : { *(.gnu.version_r)       }
+  .note.gnu.build-id : {
+    PROVIDE (__build_id_start = .);
+    *(.note.gnu.build-id)
+    PROVIDE (__build_id_end = .);
+  }
   .rel.text      :
     { *(.rel.text) *(.rel.gnu.linkonce.t*) }
   .rela.text     :

Modified: stable/12/sys/conf/ldscript.arm64
==============================================================================
--- stable/12/sys/conf/ldscript.arm64   Fri May  8 14:39:38 2020        
(r360813)
+++ stable/12/sys/conf/ldscript.arm64   Fri May  8 14:48:45 2020        
(r360814)
@@ -27,6 +27,11 @@ SECTIONS
   .gnu.version   : { *(.gnu.version)   }
   .gnu.version_d   : { *(.gnu.version_d)       }
   .gnu.version_r   : { *(.gnu.version_r)       }
+  .note.gnu.build-id : {
+    PROVIDE (__build_id_start = .);
+    *(.note.gnu.build-id)
+    PROVIDE (__build_id_end = .);
+  }
   .rel.text      :
     { *(.rel.text) *(.rel.gnu.linkonce.t*) }
   .rela.text     :

Modified: stable/12/sys/conf/ldscript.i386
==============================================================================
--- stable/12/sys/conf/ldscript.i386    Fri May  8 14:39:38 2020        
(r360813)
+++ stable/12/sys/conf/ldscript.i386    Fri May  8 14:48:45 2020        
(r360814)
@@ -62,6 +62,11 @@ SECTIONS
   PROVIDE (etext = .);
   .rodata         : { *(.rodata .rodata.* .gnu.linkonce.r.*) }
   .rodata1        : { *(.rodata1) }
+  .note.gnu.build-id : {
+    PROVIDE (__build_id_start = .);
+    *(.note.gnu.build-id)
+    PROVIDE (__build_id_end = .);
+  }
   .eh_frame_hdr : { *(.eh_frame_hdr) }
   .eh_frame       : ONLY_IF_RO { KEEP (*(.eh_frame)) }
   .gcc_except_table   : ONLY_IF_RO { *(.gcc_except_table .gcc_except_table.*) }

Modified: stable/12/sys/conf/ldscript.mips
==============================================================================
--- stable/12/sys/conf/ldscript.mips    Fri May  8 14:39:38 2020        
(r360813)
+++ stable/12/sys/conf/ldscript.mips    Fri May  8 14:48:45 2020        
(r360814)
@@ -63,6 +63,11 @@ SECTIONS
   .gnu.version   : { *(.gnu.version)   }
   .gnu.version_d   : { *(.gnu.version_d)       }
   .gnu.version_r   : { *(.gnu.version_r)       }
+  .note.gnu.build-id : {
+    PROVIDE (__build_id_start = .);
+    *(.note.gnu.build-id)
+    PROVIDE (__build_id_end = .);
+  }
   .rel.init      : { *(.rel.init)      }
   .rela.init     : { *(.rela.init)     }
   .rel.text      :

Modified: stable/12/sys/conf/ldscript.mips.cfe
==============================================================================
--- stable/12/sys/conf/ldscript.mips.cfe        Fri May  8 14:39:38 2020        
(r360813)
+++ stable/12/sys/conf/ldscript.mips.cfe        Fri May  8 14:48:45 2020        
(r360814)
@@ -192,6 +192,11 @@ SECTIONS
   PROVIDE (etext = .);
   .rodata   : { *(.rodata) *(.rodata.*) *(.gnu.linkonce.r.*) }
   .rodata1   : { *(.rodata1) }
+  .note.gnu.build-id : {
+    PROVIDE (__build_id_start = .);
+    *(.note.gnu.build-id)
+    PROVIDE (__build_id_end = .);
+  }
   .reginfo : { *(.reginfo) }
   .sdata2   : { *(.sdata2) *(.sdata2.*) *(.gnu.linkonce.s2.*) }
   .sbss2   : { *(.sbss2) *(.sbss2.*) *(.gnu.linkonce.sb2.*) }

Modified: stable/12/sys/conf/ldscript.mips.mips64
==============================================================================
--- stable/12/sys/conf/ldscript.mips.mips64     Fri May  8 14:39:38 2020        
(r360813)
+++ stable/12/sys/conf/ldscript.mips.mips64     Fri May  8 14:48:45 2020        
(r360814)
@@ -176,6 +176,11 @@ SECTIONS
   PROVIDE (etext = .);
   .rodata   : { *(.rodata) *(.rodata.*) *(.gnu.linkonce.r.*) }
   .rodata1   : { *(.rodata1) }
+  .note.gnu.build-id : {
+    PROVIDE (__build_id_start = .);
+    *(.note.gnu.build-id)
+    PROVIDE (__build_id_end = .);
+  }
   .reginfo : { *(.reginfo) }
   .sdata2   : { *(.sdata2) *(.sdata2.*) *(.gnu.linkonce.s2.*) }
   .sbss2   : { *(.sbss2) *(.sbss2.*) *(.gnu.linkonce.sb2.*) }

Modified: stable/12/sys/conf/ldscript.mips.octeon1
==============================================================================
--- stable/12/sys/conf/ldscript.mips.octeon1    Fri May  8 14:39:38 2020        
(r360813)
+++ stable/12/sys/conf/ldscript.mips.octeon1    Fri May  8 14:48:45 2020        
(r360814)
@@ -23,6 +23,12 @@ SECTIONS {
                *(.rodata)
                . = ALIGN(32);
        }
+
+       .note.gnu.build-id : {
+               PROVIDE (__build_id_start = .);
+               *(.note.gnu.build-id)
+               PROVIDE (__build_id_end = .);
+       }
        
        .data : {
                 _rwdata = .;

Modified: stable/12/sys/conf/ldscript.powerpc
==============================================================================
--- stable/12/sys/conf/ldscript.powerpc Fri May  8 14:39:38 2020        
(r360813)
+++ stable/12/sys/conf/ldscript.powerpc Fri May  8 14:48:45 2020        
(r360814)
@@ -55,6 +55,11 @@ SECTIONS
   .fini      : { *(.fini)    } =0
   .rodata    : { *(.rodata) *(.gnu.linkonce.r*) }
   .rodata1   : { *(.rodata1) }
+  .note.gnu.build-id : {
+    PROVIDE (__build_id_start = .);
+    *(.note.gnu.build-id)
+    PROVIDE (__build_id_end = .);
+  }
   .sdata2    : { *(.sdata2)  }
   .sbss2     : { *(.sbss2)   }
   /* Adjust the address for the data segment to the next page up. */

Modified: stable/12/sys/conf/ldscript.powerpc64
==============================================================================
--- stable/12/sys/conf/ldscript.powerpc64       Fri May  8 14:39:38 2020        
(r360813)
+++ stable/12/sys/conf/ldscript.powerpc64       Fri May  8 14:48:45 2020        
(r360814)
@@ -41,6 +41,11 @@ SECTIONS
   .gnu.version   : { *(.gnu.version)   }
   .gnu.version_d   : { *(.gnu.version_d)       }
   .gnu.version_r   : { *(.gnu.version_r)       }
+  .note.gnu.build-id : {
+    PROVIDE (__build_id_start = .);
+    *(.note.gnu.build-id)
+    PROVIDE (__build_id_end = .);
+  }
   .rela.text     :
     { *(.rela.text) *(.rela.gnu.linkonce.t*) }
   .rela.data     :

Modified: stable/12/sys/conf/ldscript.powerpcspe
==============================================================================
--- stable/12/sys/conf/ldscript.powerpcspe      Fri May  8 14:39:38 2020        
(r360813)
+++ stable/12/sys/conf/ldscript.powerpcspe      Fri May  8 14:48:45 2020        
(r360814)
@@ -55,6 +55,11 @@ SECTIONS
   .fini      : { *(.fini)    } =0
   .rodata    : { *(.rodata) *(.gnu.linkonce.r*) }
   .rodata1   : { *(.rodata1) }
+  .note.gnu.build-id : {
+    PROVIDE (__build_id_start = .);
+    *(.note.gnu.build-id)
+    PROVIDE (__build_id_end = .);
+  }
   .sdata2    : { *(.sdata2)  }
   .sbss2     : { *(.sbss2)   }
   /* Adjust the address for the data segment to the next page up. */

Modified: stable/12/sys/conf/ldscript.riscv
==============================================================================
--- stable/12/sys/conf/ldscript.riscv   Fri May  8 14:39:38 2020        
(r360813)
+++ stable/12/sys/conf/ldscript.riscv   Fri May  8 14:48:45 2020        
(r360814)
@@ -28,6 +28,11 @@ SECTIONS
   .gnu.version   : { *(.gnu.version)   }
   .gnu.version_d   : { *(.gnu.version_d)       }
   .gnu.version_r   : { *(.gnu.version_r)       }
+  .note.gnu.build-id : {
+    PROVIDE (__build_id_start = .);
+    *(.note.gnu.build-id)
+    PROVIDE (__build_id_end = .);
+  }
   .rel.text      :
     { *(.rel.text) *(.rel.gnu.linkonce.t*) }
   .rela.text     :

Modified: stable/12/sys/conf/ldscript.sparc64
==============================================================================
--- stable/12/sys/conf/ldscript.sparc64 Fri May  8 14:39:38 2020        
(r360813)
+++ stable/12/sys/conf/ldscript.sparc64 Fri May  8 14:48:45 2020        
(r360814)
@@ -146,6 +146,11 @@ SECTIONS
   PROVIDE (etext = .);
   .rodata   : { *(.rodata) *(.rodata.*) *(.gnu.linkonce.r.*) }
   .rodata1   : { *(.rodata1) }
+  .note.gnu.build-id : {
+    PROVIDE (__build_id_start = .);
+    *(.note.gnu.build-id)
+    PROVIDE (__build_id_end = .);
+  }
   .sdata2   : { *(.sdata2) *(.sdata2.*) *(.gnu.linkonce.s2.*) }
   .sbss2   : { *(.sbss2) *(.sbss2.*) *(.gnu.linkonce.sb2.*) }
   . = ALIGN(0x2000) + (. & (0x2000 - 1));

Modified: stable/12/sys/kern/kern_mib.c
==============================================================================
--- stable/12/sys/kern/kern_mib.c       Fri May  8 14:39:38 2020        
(r360813)
+++ stable/12/sys/kern/kern_mib.c       Fri May  8 14:48:45 2020        
(r360814)
@@ -491,6 +491,54 @@ SYSCTL_PROC(_kern, KERN_OSRELDATE, osreldate,
     CTLTYPE_INT | CTLFLAG_CAPRD | CTLFLAG_RD | CTLFLAG_MPSAFE,
     NULL, 0, sysctl_osreldate, "I", "Kernel release date");
 
+/*
+ * The build-id is copied from the ELF section .note.gnu.build-id.  The linker 
+ * script defines two variables to expose the beginning and end.  LLVM 
+ * currently uses a SHA-1 hash, but other formats can be supported by checking 
+ * the length of the section.
+ */
+
+extern char __build_id_start[];
+extern char __build_id_end[];
+
+#define        BUILD_ID_HEADER_LEN     0x10
+#define        BUILD_ID_HASH_MAXLEN    0x14
+
+static int
+sysctl_build_id(SYSCTL_HANDLER_ARGS)
+{
+       uintptr_t sectionlen = (uintptr_t)(__build_id_end - __build_id_start);
+       int hashlen;
+       char buf[2*BUILD_ID_HASH_MAXLEN+1];
+
+       /*
+        * The ELF note section has a four byte length for the vendor name,
+        * four byte length for the value, and a four byte vendor specific 
+        * type.  The name for the build id is "GNU\0".  We skip the first 16 
+        * bytes to read the build hash.  We will return the remaining bytes up 
+        * to 20 (SHA-1) hash size.  If the hash happens to be a custom number 
+        * of bytes we will pad the value with zeros, as the section should be 
+        * four byte aligned.
+        */
+       if (sectionlen <= BUILD_ID_HEADER_LEN ||
+           sectionlen > (BUILD_ID_HEADER_LEN + BUILD_ID_HASH_MAXLEN)) {
+           return (ENOENT);
+       }
+   
+
+       hashlen = sectionlen - BUILD_ID_HEADER_LEN;
+       for (int i = 0; i < hashlen; i++) {
+           uint8_t c = __build_id_start[i+BUILD_ID_HEADER_LEN];
+           snprintf(&buf[2*i], 3, "%02x", c);
+       }
+
+       return (SYSCTL_OUT(req, buf, strlen(buf) + 1));
+}
+
+SYSCTL_PROC(_kern, OID_AUTO, build_id,
+    CTLTYPE_STRING | CTLFLAG_CAPRD | CTLFLAG_RD | CTLFLAG_MPSAFE,
+    NULL, 0, sysctl_build_id, "A", "Operating system build-id");
+
 SYSCTL_NODE(_kern, OID_AUTO, features, CTLFLAG_RD, 0, "Kernel Features");
 
 #ifdef COMPAT_FREEBSD4
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