[build] Fix %.licence build target

Our use of --gc-sections causes the linker to discard the symbols
defined by FILE_LICENCE(), meaning that the resulting licence
determination is incomplete.

We must use the KEEP() directive in the linker script to force the
linker to not discard the licence symbols.  Using KEEP(*(COMMON))
would be undesirable, since there are some symbols in COMMON which we
may wish to discard.

Fix by placing symbols defined by PROVIDE_SYMBOL() (which is used by
FILE_LICENCE()) into a special ".provided" section, which we then mark
with KEEP().  All such symbols are zero-length, so there is no cost in
terms of the final binary size.

Since the symbols are no longer in COMMON, the linker will reject
symbols with the same name coming from multiple objects.  We therefore
append the object name to the licence symbol, to ensure that it is
unique.

Reported-by: Marin Hannache <git@mareo.fr>
Signed-off-by: Michael Brown <mcb30@ipxe.org>

3 files changed, 6 insertions, 0 deletions

diff --git a/src/arch/i386/scripts/i386-kir.lds b/src/arch/i386/scripts/i386-kir.lds
index 338d6ee8..66bf804e 100644
--- a/src/arch/i386/scripts/i386-kir.lds
+++ b/src/arch/i386/scripts/i386-kir.lds
@@ -98,6 +98,8 @@ SECTIONS {
 	*(.data)
 	*(.data.*)
 	KEEP(*(SORT(.tbl.*)))	/* Various tables.  See include/tables.h */
+	KEEP(*(.provided))
+	KEEP(*(.provided.*))
 	_edata16_progbits = .;
     }
     .bss16 : AT ( _data16_load_offset + __bss16 ) {
diff --git a/src/arch/i386/scripts/i386.lds b/src/arch/i386/scripts/i386.lds
index fb763656..98f95cb2 100644
--- a/src/arch/i386/scripts/i386.lds
+++ b/src/arch/i386/scripts/i386.lds
@@ -109,6 +109,8 @@ SECTIONS {
 	*(.data)
 	*(.data.*)
 	KEEP(*(SORT(.tbl.*)))	/* Various tables.  See include/tables.h */
+	KEEP(*(.provided))
+	KEEP(*(.provided.*))
 	_mtextdata = .;
     } .bss.textdata (NOLOAD) : AT ( _end_lma ) {
 	*(.bss)
diff --git a/src/arch/i386/scripts/linux.lds b/src/arch/i386/scripts/linux.lds
index 64c9b97f..9f2eeaf3 100644
--- a/src/arch/i386/scripts/linux.lds
+++ b/src/arch/i386/scripts/linux.lds
@@ -53,6 +53,8 @@ SECTIONS {
 		*(.data)
 		*(.data.*)
 		KEEP(*(SORT(.tbl.*)))
+		KEEP(*(.provided))
+		KEEP(*(.provided.*))
 		_edata = .;
 	}