linux-kernel - [PATCH 1/1] PCI: Optimize pci_resource_len() to reduce the binary size of kernel

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Date:   Tue, 13 Jul 2021 15:22:36 +0800
From:   Zhen Lei <thunder.leizhen@...wei.com>
To:     Bjorn Helgaas <bhelgaas@...gle.com>,
        linux-pci <linux-pci@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>
CC:     Zhen Lei <thunder.leizhen@...wei.com>
Subject: [PATCH 1/1] PCI: Optimize pci_resource_len() to reduce the binary size of kernel

pci_resource_end() can be 0 only when pci_resource_start() is 0.
Otherwise, it is definitely an error. In this case, pci_resource_len()
should be regarded as 0. Therefore, determining whether
pci_resource_start() and pci_resource_end() are both 0 can be reduced to
determining only whether pci_resource_end() is 0.

Although only one condition judgment is reduced, the macro function
pci_resource_len() is widely referenced in the kernel. I used defconfig to
compile the latest kernel on X86, and its binary code size was reduced by
about 3KB.

Before:
 [ 2] .rela.text        RELA             0000000000000000  093bfcb0
      0000000001a67168  0000000000000018   I      68     1     8

After:
 [ 2] .rela.text        RELA             0000000000000000  093bfcb0
      0000000001a66598  0000000000000018   I      68     1     8

Signed-off-by: Zhen Lei <thunder.leizhen@...wei.com>
---
 include/linux/pci.h | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/include/linux/pci.h b/include/linux/pci.h
index 540b377ca8f6..23ef1a15eb5d 100644
--- a/include/linux/pci.h
+++ b/include/linux/pci.h
@@ -1881,9 +1881,7 @@ int pci_iobar_pfn(struct pci_dev *pdev, int bar, struct vm_area_struct *vma);
 #define pci_resource_end(dev, bar)	((dev)->resource[(bar)].end)
 #define pci_resource_flags(dev, bar)	((dev)->resource[(bar)].flags)
 #define pci_resource_len(dev,bar) \
-	((pci_resource_start((dev), (bar)) == 0 &&	\
-	  pci_resource_end((dev), (bar)) ==		\
-	  pci_resource_start((dev), (bar))) ? 0 :	\
+	((pci_resource_end((dev), (bar)) == 0) ? 0 :	\
 							\
 	 (pci_resource_end((dev), (bar)) -		\
 	  pci_resource_start((dev), (bar)) + 1))
-- 
2.25.1